style.py

"""
Module for applying conditional formatting to
DataFrames and Series.
"""
from functools import partial
from itertools import product
from contextlib import contextmanager
from uuid import uuid1
import copy
from collections import defaultdict, MutableMapping

try:
    from jinja2 import Template
except ImportError:
    msg = "pandas.Styler requires jinja2. "\
          "Please install with `conda install Jinja2`\n"\
          "or `pip install Jinja2`"
    raise ImportError(msg)

from pandas.types.common import is_float, is_string_like

import numpy as np
import pandas as pd
from pandas.compat import range
from pandas.core.config import get_option
import pandas.core.common as com
from pandas.core.indexing import _maybe_numeric_slice, _non_reducing_slice
try:
    import matplotlib.pyplot as plt
    from matplotlib import colors
    has_mpl = True
except ImportError:
    has_mpl = False
    no_mpl_message = "{0} requires matplotlib."


@contextmanager
def _mpl(func):
    if has_mpl:
        yield plt, colors
    else:
        raise ImportError(no_mpl_message.format(func.__name__))


class Styler(object):
    """
    Helps style a DataFrame or Series according to the
    data with HTML and CSS.

    .. versionadded:: 0.17.1

    .. warning::
        This is a new feature and is under active development.
        We'll be adding features and possibly making breaking changes in future
        releases.

    Parameters
    ----------
    data: Series or DataFrame
    precision: int
        precision to round floats to, defaults to pd.options.display.precision
    table_styles: list-like, default None
        list of {selector: (attr, value)} dicts; see Notes
    uuid: str, default None
        a unique identifier to avoid CSS collisons; generated automatically
    caption: str, default None
        caption to attach to the table

    Attributes
    ----------
    template: Jinja Template

    Notes
    -----
    Most styling will be done by passing style functions into
    ``Styler.apply`` or ``Styler.applymap``. Style functions should
    return values with strings containing CSS ``'attr: value'`` that will
    be applied to the indicated cells.

    If using in the Jupyter notebook, Styler has defined a ``_repr_html_``
    to automatically render itself. Otherwise call Styler.render to get
    the genterated HTML.

    CSS classes are attached to the generated HTML

    * Index and Column names include ``index_name`` and ``level<k>``
      where `k` is its level in a MultiIndex
    * Index label cells include

      * ``row_heading``
      * ``row<n>`` where `n` is the numeric position of the row
      * ``level<k>`` where `k` is the level in a MultiIndex

    * Column label cells include
      * ``col_heading``
      * ``col<n>`` where `n` is the numeric position of the column
      * ``evel<k>`` where `k` is the level in a MultiIndex

    * Blank cells include ``blank``
    * Data cells include ``data``

    See Also
    --------
    pandas.DataFrame.style
    """
    template = Template("""
        <style  type="text/css" >
        {% for s in table_styles %}
            #T_{{uuid}} {{s.selector}} {
            {% for p,val in s.props %}
                {{p}}: {{val}};
            {% endfor %}
            }
        {% endfor %}
        {% for s in cellstyle %}
            #T_{{uuid}}{{s.selector}} {
            {% for p,val in s.props %}
                {{p}}: {{val}};
            {% endfor %}
            }
        {% endfor %}
        </style>

        <table id="T_{{uuid}}" {{ table_attributes }}>
        {% if caption %}
            <caption>{{caption}}</caption>
        {% endif %}

        <thead>
            {% for r in head %}
            <tr>
                {% for c in r %}
                {% if c.is_visible != False %}
                <{{c.type}} class="{{c.class}}" {{ c.attributes|join(" ") }}>
                  {{c.value}}
                {% endif %}
                {% endfor %}
            </tr>
            {% endfor %}
        </thead>
        <tbody>
            {% for r in body %}
            <tr>
                {% for c in r %}
                {% if c.is_visible != False %}
                <{{c.type}} id="T_{{uuid}}{{c.id}}"
                 class="{{c.class}}" {{ c.attributes|join(" ") }}>
                    {{ c.display_value }}
                {% endif %}
                {% endfor %}
            </tr>
            {% endfor %}
        </tbody>
        </table>
        """)

    def __init__(self, data, precision=None, table_styles=None, uuid=None,
                 caption=None, table_attributes=None):
        self.ctx = defaultdict(list)
        self._todo = []

        if not isinstance(data, (pd.Series, pd.DataFrame)):
            raise TypeError("``data`` must be a Series or DataFrame")
        if data.ndim == 1:
            data = data.to_frame()
        if not data.index.is_unique or not data.columns.is_unique:
            raise ValueError("style is not supported for non-unique indicies.")

        self.data = data
        self.index = data.index
        self.columns = data.columns

        self.uuid = uuid
        self.table_styles = table_styles
        self.caption = caption
        if precision is None:
            precision = get_option('display.precision')
        self.precision = precision
        self.table_attributes = table_attributes
        # display_funcs maps (row, col) -> formatting function

        def default_display_func(x):
            if is_float(x):
                return '{:>.{precision}g}'.format(x, precision=self.precision)
            else:
                return x

        self._display_funcs = defaultdict(lambda: default_display_func)

    def _repr_html_(self):
        """Hooks into Jupyter notebook rich display system."""
        return self.render()

    def _translate(self):
        """
        Convert the DataFrame in `self.data` and the attrs from `_build_styles`
        into a dictionary of {head, body, uuid, cellstyle}
        """
        table_styles = self.table_styles or []
        caption = self.caption
        ctx = self.ctx
        precision = self.precision
        uuid = self.uuid or str(uuid1()).replace("-", "_")
        ROW_HEADING_CLASS = "row_heading"
        COL_HEADING_CLASS = "col_heading"
        INDEX_NAME_CLASS = "index_name"

        DATA_CLASS = "data"
        BLANK_CLASS = "blank"
        BLANK_VALUE = ""

        def format_attr(pair):
            return "{key}={value}".format(**pair)

        # for sparsifying a MultiIndex
        idx_lengths = _get_level_lengths(self.index)
        col_lengths = _get_level_lengths(self.columns)

        cell_context = dict()

        n_rlvls = self.data.index.nlevels
        n_clvls = self.data.columns.nlevels
        rlabels = self.data.index.tolist()
        clabels = self.data.columns.tolist()

        if n_rlvls == 1:
            rlabels = [[x] for x in rlabels]
        if n_clvls == 1:
            clabels = [[x] for x in clabels]
        clabels = list(zip(*clabels))

        cellstyle = []
        head = []

        for r in range(n_clvls):
            # Blank for Index columns...
            row_es = [{"type": "th",
                       "value": BLANK_VALUE,
                       "display_value": BLANK_VALUE,
                       "is_visible": True,
                       "class": " ".join([BLANK_CLASS])}] * (n_rlvls - 1)

            # ... except maybe the last for columns.names
            name = self.data.columns.names[r]
            cs = [BLANK_CLASS if name is None else INDEX_NAME_CLASS,
                  "level%s" % r]
            name = BLANK_VALUE if name is None else name
            row_es.append({"type": "th",
                           "value": name,
                           "display_value": name,
                           "class": " ".join(cs),
                           "is_visible": True})

            for c, value in enumerate(clabels[r]):
                cs = [COL_HEADING_CLASS, "level%s" % r, "col%s" % c]
                cs.extend(cell_context.get(
                    "col_headings", {}).get(r, {}).get(c, []))
                es = {
                    "type": "th",
                    "value": value,
                    "display_value": value,
                    "class": " ".join(cs),
                    "is_visible": _is_visible(c, r, col_lengths),
                }
                colspan = col_lengths.get((r, c), 0)
                if colspan > 1:
                    es["attributes"] = [
                        format_attr({"key": "colspan", "value": colspan})
                    ]
                row_es.append(es)
            head.append(row_es)

        if self.data.index.names and not all(x is None
                                             for x in self.data.index.names):
            index_header_row = []

            for c, name in enumerate(self.data.index.names):
                cs = [INDEX_NAME_CLASS,
                      "level%s" % c]
                name = '' if name is None else name
                index_header_row.append({"type": "th", "value": name,
                                         "class": " ".join(cs)})

            index_header_row.extend(
                [{"type": "th",
                  "value": BLANK_VALUE,
                  "class": " ".join([BLANK_CLASS])
                  }] * len(clabels[0]))

            head.append(index_header_row)

        body = []
        for r, idx in enumerate(self.data.index):
            row_es = []
            for c, value in enumerate(rlabels[r]):
                es = {
                    "type": "th",
                    "is_visible": _is_visible(r, c, idx_lengths),
                    "value": value,
                    "display_value": value,
                    "class": " ".join([ROW_HEADING_CLASS, "level%s" % c,
                                       "row%s" % r]),
                }
                rowspan = idx_lengths.get((c, r), 0)
                if rowspan > 1:
                    es["attributes"] = [
                        format_attr({"key": "rowspan", "value": rowspan})
                    ]
                row_es.append(es)

            for c, col in enumerate(self.data.columns):
                cs = [DATA_CLASS, "row%s" % r, "col%s" % c]
                cs.extend(cell_context.get("data", {}).get(r, {}).get(c, []))
                formatter = self._display_funcs[(r, c)]
                value = self.data.iloc[r, c]
                row_es.append({
                    "type": "td",
                    "value": value,
                    "class": " ".join(cs),
                    "id": "_".join(cs[1:]),
                    "display_value": formatter(value)
                })
                props = []
                for x in ctx[r, c]:
                    # have to handle empty styles like ['']
                    if x.count(":"):
                        props.append(x.split(":"))
                    else:
                        props.append(['', ''])
                cellstyle.append({'props': props,
                                  'selector': "row%s_col%s" % (r, c)})
            body.append(row_es)

        return dict(head=head, cellstyle=cellstyle, body=body, uuid=uuid,
                    precision=precision, table_styles=table_styles,
                    caption=caption, table_attributes=self.table_attributes)

    def format(self, formatter, subset=None):
        """
        Format the text display value of cells.

        .. versionadded:: 0.18.0

        Parameters
        ----------
        formatter: str, callable, or dict
        subset: IndexSlice
            An argument to ``DataFrame.loc`` that restricts which elements
            ``formatter`` is applied to.

        Returns
        -------
        self : Styler

        Notes
        -----

        ``formatter`` is either an ``a`` or a dict ``{column name: a}`` where
        ``a`` is one of

        - str: this will be wrapped in: ``a.format(x)``
        - callable: called with the value of an individual cell

        The default display value for numeric values is the "general" (``g``)
        format with ``pd.options.display.precision`` precision.

        Examples
        --------

        >>> df = pd.DataFrame(np.random.randn(4, 2), columns=['a', 'b'])
        >>> df.style.format("{:.2%}")
        >>> df['c'] = ['a', 'b', 'c', 'd']
        >>> df.style.format({'C': str.upper})
        """
        if subset is None:
            row_locs = range(len(self.data))
            col_locs = range(len(self.data.columns))
        else:
            subset = _non_reducing_slice(subset)
            if len(subset) == 1:
                subset = subset, self.data.columns

            sub_df = self.data.loc[subset]
            row_locs = self.data.index.get_indexer_for(sub_df.index)
            col_locs = self.data.columns.get_indexer_for(sub_df.columns)

        if isinstance(formatter, MutableMapping):
            for col, col_formatter in formatter.items():
                # formatter must be callable, so '{}' are converted to lambdas
                col_formatter = _maybe_wrap_formatter(col_formatter)
                col_num = self.data.columns.get_indexer_for([col])[0]

                for row_num in row_locs:
                    self._display_funcs[(row_num, col_num)] = col_formatter
        else:
            # single scalar to format all cells with
            locs = product(*(row_locs, col_locs))
            for i, j in locs:
                formatter = _maybe_wrap_formatter(formatter)
                self._display_funcs[(i, j)] = formatter
        return self

    def render(self):
        """
        Render the built up styles to HTML

        .. versionadded:: 0.17.1

        Returns
        -------
        rendered: str
            the rendered HTML

        Notes
        -----
        ``Styler`` objects have defined the ``_repr_html_`` method
        which automatically calls ``self.render()`` when it's the
        last item in a Notebook cell. When calling ``Styler.render()``
        directly, wrap the result in ``IPython.display.HTML`` to view
        the rendered HTML in the notebook.
        """
        self._compute()
        d = self._translate()
        # filter out empty styles, every cell will have a class
        # but the list of props may just be [['', '']].
        # so we have the neested anys below
        trimmed = [x for x in d['cellstyle']
                   if any(any(y) for y in x['props'])]
        d['cellstyle'] = trimmed
        return self.template.render(**d)

    def _update_ctx(self, attrs):
        """
        update the state of the Styler. Collects a mapping
        of {index_label: ['<property>: <value>']}

        attrs: Series or DataFrame
        should contain strings of '<property>: <value>;<prop2>: <val2>'
        Whitespace shouldn't matter and the final trailing ';' shouldn't
        matter.
        """
        for row_label, v in attrs.iterrows():
            for col_label, col in v.iteritems():
                i = self.index.get_indexer([row_label])[0]
                j = self.columns.get_indexer([col_label])[0]
                for pair in col.rstrip(";").split(";"):
                    self.ctx[(i, j)].append(pair)

    def _copy(self, deepcopy=False):
        styler = Styler(self.data, precision=self.precision,
                        caption=self.caption, uuid=self.uuid,
                        table_styles=self.table_styles)
        if deepcopy:
            styler.ctx = copy.deepcopy(self.ctx)
            styler._todo = copy.deepcopy(self._todo)
        else:
            styler.ctx = self.ctx
            styler._todo = self._todo
        return styler

    def __copy__(self):
        """
        Deep copy by default.
        """
        return self._copy(deepcopy=False)

    def __deepcopy__(self, memo):
        return self._copy(deepcopy=True)

    def clear(self):
        """"Reset" the styler, removing any previously applied styles.
        Returns None.
        """
        self.ctx.clear()
        self._todo = []

    def _compute(self):
        """
        Execute the style functions built up in `self._todo`.

        Relies on the conventions that all style functions go through
        .apply or .applymap. The append styles to apply as tuples of

        (application method, *args, **kwargs)
        """
        r = self
        for func, args, kwargs in self._todo:
            r = func(self)(*args, **kwargs)
        return r

    def _apply(self, func, axis=0, subset=None, **kwargs):
        subset = slice(None) if subset is None else subset
        subset = _non_reducing_slice(subset)
        data = self.data.loc[subset]
        if axis is not None:
            result = data.apply(func, axis=axis, **kwargs)
        else:
            result = func(data, **kwargs)
            if not isinstance(result, pd.DataFrame):
                raise TypeError(
                    "Function {!r} must return a DataFrame when "
                    "passed to `Styler.apply` with axis=None".format(func))
            if not (result.index.equals(data.index) and
                    result.columns.equals(data.columns)):
                msg = ('Result of {!r} must have identical index and columns '
                       'as the input'.format(func))
                raise ValueError(msg)

        result_shape = result.shape
        expected_shape = self.data.loc[subset].shape
        if result_shape != expected_shape:
            msg = ("Function {!r} returned the wrong shape.\n"
                   "Result has shape: {}\n"
                   "Expected shape:   {}".format(func,
                                                 result.shape,
                                                 expected_shape))
            raise ValueError(msg)
        self._update_ctx(result)
        return self

    def apply(self, func, axis=0, subset=None, **kwargs):
        """
        Apply a function column-wise, row-wise, or table-wase,
        updating the HTML representation with the result.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        func : function
            ``func`` should take a Series or DataFrame (depending
            on ``axis``), and return an object with the same shape.
            Must return a DataFrame with identical index and
            column labels when ``axis=None``
        axis : int, str or None
            apply to each column (``axis=0`` or ``'index'``)
            or to each row (``axis=1`` or ``'columns'``) or
            to the entire DataFrame at once with ``axis=None``
        subset : IndexSlice
            a valid indexer to limit ``data`` to *before* applying the
            function. Consider using a pandas.IndexSlice
        kwargs : dict
            pass along to ``func``

        Returns
        -------
        self : Styler

        Notes
        -----
        The output shape of ``func`` should match the input, i.e. if
        ``x`` is the input row, column, or table (depending on ``axis``),
        then ``func(x.shape) == x.shape`` should be true.

        This is similar to ``DataFrame.apply``, except that ``axis=None``
        applies the function to the entire DataFrame at once,
        rather than column-wise or row-wise.

        Examples
        --------
        >>> def highlight_max(x):
        ...     return ['background-color: yellow' if v == x.max() else ''
                        for v in x]
        ...
        >>> df = pd.DataFrame(np.random.randn(5, 2))
        >>> df.style.apply(highlight_max)
        """
        self._todo.append((lambda instance: getattr(instance, '_apply'),
                           (func, axis, subset), kwargs))
        return self

    def _applymap(self, func, subset=None, **kwargs):
        func = partial(func, **kwargs)  # applymap doesn't take kwargs?
        if subset is None:
            subset = pd.IndexSlice[:]
        subset = _non_reducing_slice(subset)
        result = self.data.loc[subset].applymap(func)
        self._update_ctx(result)
        return self

    def applymap(self, func, subset=None, **kwargs):
        """
        Apply a function elementwise, updating the HTML
        representation with the result.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        func : function
            ``func`` should take a scalar and return a scalar
        subset : IndexSlice
            a valid indexer to limit ``data`` to *before* applying the
            function. Consider using a pandas.IndexSlice
        kwargs : dict
            pass along to ``func``

        Returns
        -------
        self : Styler

        """
        self._todo.append((lambda instance: getattr(instance, '_applymap'),
                           (func, subset), kwargs))
        return self

    def set_precision(self, precision):
        """
        Set the precision used to render.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        precision: int

        Returns
        -------
        self : Styler
        """
        self.precision = precision
        return self

    def set_table_attributes(self, attributes):
        """
        Set the table attributes. These are the items
        that show up in the opening ``<table>`` tag in addition
        to to automatic (by default) id.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        attributes : string

        Returns
        -------
        self : Styler

        Examples
        --------
        >>> df = pd.DataFrame(np.random.randn(10, 4))
        >>> df.style.set_table_attributes('class="pure-table"')
        # ... <table class="pure-table"> ...
        """
        self.table_attributes = attributes
        return self

    def export(self):
        """
        Export the styles to applied to the current Styler.
        Can be applied to a second style with ``Styler.use``.

        .. versionadded:: 0.17.1

        Returns
        -------
        styles: list

        See Also
        --------
        Styler.use
        """
        return self._todo

    def use(self, styles):
        """
        Set the styles on the current Styler, possibly using styles
        from ``Styler.export``.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        styles: list
            list of style functions

        Returns
        -------
        self : Styler

        See Also
        --------
        Styler.export
        """
        self._todo.extend(styles)
        return self

    def set_uuid(self, uuid):
        """
        Set the uuid for a Styler.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        uuid: str

        Returns
        -------
        self : Styler
        """
        self.uuid = uuid
        return self

    def set_caption(self, caption):
        """
        Se the caption on a Styler

        .. versionadded:: 0.17.1

        Parameters
        ----------
        caption: str

        Returns
        -------
        self : Styler
        """
        self.caption = caption
        return self

    def set_table_styles(self, table_styles):
        """
        Set the table styles on a Styler. These are placed in a
        ``<style>`` tag before the generated HTML table.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        table_styles: list
            Each individual table_style should be a dictionary with
            ``selector`` and ``props`` keys. ``selector`` should be a CSS
            selector that the style will be applied to (automatically
            prefixed by the table's UUID) and ``props`` should be a list of
            tuples with ``(attribute, value)``.

        Returns
        -------
        self : Styler

        Examples
        --------
        >>> df = pd.DataFrame(np.random.randn(10, 4))
        >>> df.style.set_table_styles(
        ...     [{'selector': 'tr:hover',
        ...       'props': [('background-color', 'yellow')]}]
        ... )
        """
        self.table_styles = table_styles
        return self

    # -----------------------------------------------------------------------
    # A collection of "builtin" styles
    # -----------------------------------------------------------------------

    @staticmethod
    def _highlight_null(v, null_color):
        return 'background-color: %s' % null_color if pd.isnull(v) else ''

    def highlight_null(self, null_color='red'):
        """
        Shade the background ``null_color`` for missing values.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        null_color: str

        Returns
        -------
        self : Styler
        """
        self.applymap(self._highlight_null, null_color=null_color)
        return self

    def background_gradient(self, cmap='PuBu', low=0, high=0, axis=0,
                            subset=None):
        """
        Color the background in a gradient according to
        the data in each column (optionally row).
        Requires matplotlib.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        cmap: str or colormap
            matplotlib colormap
        low, high: float
            compress the range by these values.
        axis: int or str
            1 or 'columns' for columnwise, 0 or 'index' for rowwise
        subset: IndexSlice
            a valid slice for ``data`` to limit the style application to

        Returns
        -------
        self : Styler

        Notes
        -----
        Tune ``low`` and ``high`` to keep the text legible by
        not using the entire range of the color map. These extend
        the range of the data by ``low * (x.max() - x.min())``
        and ``high * (x.max() - x.min())`` before normalizing.
        """
        subset = _maybe_numeric_slice(self.data, subset)
        subset = _non_reducing_slice(subset)
        self.apply(self._background_gradient, cmap=cmap, subset=subset,
                   axis=axis, low=low, high=high)
        return self

    @staticmethod
    def _background_gradient(s, cmap='PuBu', low=0, high=0):
        """Color background in a range according to the data."""
        with _mpl(Styler.background_gradient) as (plt, colors):
            rng = s.max() - s.min()
            # extend lower / upper bounds, compresses color range
            norm = colors.Normalize(s.min() - (rng * low),
                                    s.max() + (rng * high))
            # matplotlib modifies inplace?
            # https://github.com/matplotlib/matplotlib/issues/5427
            normed = norm(s.values)
            c = [colors.rgb2hex(x) for x in plt.cm.get_cmap(cmap)(normed)]
            return ['background-color: %s' % color for color in c]

    def set_properties(self, subset=None, **kwargs):
        """
        Convience method for setting one or more non-data dependent
        properties or each cell.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        subset: IndexSlice
            a valid slice for ``data`` to limit the style application to
        kwargs: dict
            property: value pairs to be set for each cell

        Returns
        -------
        self : Styler

        Examples
        --------
        >>> df = pd.DataFrame(np.random.randn(10, 4))
        >>> df.style.set_properties(color="white", align="right")
        >>> df.style.set_properties(**{'background-color': 'yellow'})
        """
        values = ';'.join('{p}: {v}'.format(p=p, v=v)
                          for p, v in kwargs.items())
        f = lambda x: values
        return self.applymap(f, subset=subset)

    @staticmethod
    def _bar(s, color, width):
        normed = width * (s - s.min()) / (s.max() - s.min())

        base = 'width: 10em; height: 80%;'
        attrs = (base + 'background: linear-gradient(90deg,{c} {w}%, '
                        'transparent 0%)')
        return [attrs.format(c=color, w=x) if x != 0 else base for x in normed]

    def bar(self, subset=None, axis=0, color='#d65f5f', width=100):
        """
        Color the background ``color`` proptional to the values in each column.
        Excludes non-numeric data by default.

        .. versionadded:: 0.17.1

        Parameters
        ----------
        subset: IndexSlice, default None
            a valid slice for ``data`` to limit the style application to
        axis: int
        color: str
        width: float
            A number between 0 or 100. The largest value will cover ``width``
            percent of the cell's width

        Returns
        -------
        self : Styler
        """
        subset = _maybe_numeric_slice(self.data, subset)
        subset = _non_reducing_slice(subset)
        self.apply(self._bar, subset=subset, axis=axis, color=color,
                   width=width)
        return self

    def highlight_max(self, subset=None, color='yellow', axis=0):
        """
        Highlight the maximum by shading the background

        .. versionadded:: 0.17.1

        Parameters
        ----------
        subset: IndexSlice, default None
            a valid slice for ``data`` to limit the style application to
        color: str, default 'yellow'
        axis: int, str, or None; default None
            0 or 'index' for columnwise, 1 or 'columns' for rowwise
            or ``None`` for tablewise (the default)

        Returns
        -------
        self : Styler
        """
        return self._highlight_handler(subset=subset, color=color, axis=axis,
                                       max_=True)

    def highlight_min(self, subset=None, color='yellow', axis=0):
        """
        Highlight the minimum by shading the background

        .. versionadded:: 0.17.1

        Parameters
        ----------
        subset: IndexSlice, default None
            a valid slice for ``data`` to limit the style application to
        color: str, default 'yellow'
        axis: int, str, or None; default None
            0 or 'index' for columnwise, 1 or 'columns' for rowwise
            or ``None`` for tablewise (the default)

        Returns
        -------
        self : Styler
        """
        return self._highlight_handler(subset=subset, color=color, axis=axis,
                                       max_=False)

    def _highlight_handler(self, subset=None, color='yellow', axis=None,
                           max_=True):
        subset = _non_reducing_slice(_maybe_numeric_slice(self.data, subset))
        self.apply(self._highlight_extrema, color=color, axis=axis,
                   subset=subset, max_=max_)
        return self

    @staticmethod
    def _highlight_extrema(data, color='yellow', max_=True):
        """Highlight the min or max in a Series or DataFrame"""
        attr = 'background-color: {0}'.format(color)
        if data.ndim == 1:  # Series from .apply
            if max_:
                extrema = data == data.max()
            else:
                extrema = data == data.min()
            return [attr if v else '' for v in extrema]
        else:  # DataFrame from .tee
            if max_:
                extrema = data == data.max().max()
            else:
                extrema = data == data.min().min()
            return pd.DataFrame(np.where(extrema, attr, ''),
                                index=data.index, columns=data.columns)


def _is_visible(idx_row, idx_col, lengths):
    """
    Index -> {(idx_row, idx_col): bool})
    """
    return (idx_col, idx_row) in lengths


def _get_level_lengths(index):
    """
    Given an index, find the level lenght for each element.

    Result is a dictionary of (level, inital_position): span
    """
    sentinel = com.sentinel_factory()
    levels = index.format(sparsify=sentinel, adjoin=False, names=False)

    if index.nlevels == 1:
        return {(0, i): 1 for i, value in enumerate(levels)}

    lengths = {}

    for i, lvl in enumerate(levels):
        for j, row in enumerate(lvl):
            if not get_option('display.multi_sparse'):
                lengths[(i, j)] = 1
            elif row != sentinel:
                last_label = j
                lengths[(i, last_label)] = 1
            else:
                lengths[(i, last_label)] += 1

    return lengths


def _maybe_wrap_formatter(formatter):
    if is_string_like(formatter):
        return lambda x: formatter.format(x)
    elif callable(formatter):
        return formatter
    else:
        msg = "Expected a template string or callable, got {} instead".format(
            formatter)
        raise TypeError(msg)