/
reshape.py
1333 lines (1093 loc) · 44.6 KB
/
reshape.py
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# pylint: disable=E1101,E1103
# pylint: disable=W0703,W0622,W0613,W0201
from pandas.compat import range, zip
from pandas import compat
import itertools
import re
import numpy as np
from pandas.core.dtypes.common import (
_ensure_platform_int,
is_list_like, is_bool_dtype,
needs_i8_conversion)
from pandas.core.dtypes.cast import maybe_promote
from pandas.core.dtypes.missing import notnull
import pandas.core.dtypes.concat as _concat
from pandas.core.series import Series
from pandas.core.frame import DataFrame
from pandas.core.sparse.api import SparseDataFrame, SparseSeries
from pandas.core.sparse.array import SparseArray
from pandas._libs.sparse import IntIndex
from pandas.core.categorical import Categorical, _factorize_from_iterable
from pandas.core.sorting import (get_group_index, get_compressed_ids,
compress_group_index, decons_obs_group_ids)
import pandas.core.algorithms as algos
from pandas._libs import algos as _algos, reshape as _reshape
from pandas.core.frame import _shared_docs
from pandas.util._decorators import Appender
from pandas.core.index import MultiIndex, _get_na_value
class _Unstacker(object):
"""
Helper class to unstack data / pivot with multi-level index
Parameters
----------
level : int or str, default last level
Level to "unstack". Accepts a name for the level.
Examples
--------
>>> import pandas as pd
>>> index = pd.MultiIndex.from_tuples([('one', 'a'), ('one', 'b'),
... ('two', 'a'), ('two', 'b')])
>>> s = pd.Series(np.arange(1.0, 5.0), index=index)
>>> s
one a 1
b 2
two a 3
b 4
dtype: float64
>>> s.unstack(level=-1)
a b
one 1 2
two 3 4
>>> s.unstack(level=0)
one two
a 1 2
b 3 4
Returns
-------
unstacked : DataFrame
"""
def __init__(self, values, index, level=-1, value_columns=None,
fill_value=None):
self.is_categorical = None
if values.ndim == 1:
if isinstance(values, Categorical):
self.is_categorical = values
values = np.array(values)
values = values[:, np.newaxis]
self.values = values
self.value_columns = value_columns
self.fill_value = fill_value
if value_columns is None and values.shape[1] != 1: # pragma: no cover
raise ValueError('must pass column labels for multi-column data')
self.index = index
if isinstance(self.index, MultiIndex):
if index._reference_duplicate_name(level):
msg = ("Ambiguous reference to {0}. The index "
"names are not unique.".format(level))
raise ValueError(msg)
self.level = self.index._get_level_number(level)
# when index includes `nan`, need to lift levels/strides by 1
self.lift = 1 if -1 in self.index.labels[self.level] else 0
self.new_index_levels = list(index.levels)
self.new_index_names = list(index.names)
self.removed_name = self.new_index_names.pop(self.level)
self.removed_level = self.new_index_levels.pop(self.level)
self._make_sorted_values_labels()
self._make_selectors()
def _make_sorted_values_labels(self):
v = self.level
labs = list(self.index.labels)
levs = list(self.index.levels)
to_sort = labs[:v] + labs[v + 1:] + [labs[v]]
sizes = [len(x) for x in levs[:v] + levs[v + 1:] + [levs[v]]]
comp_index, obs_ids = get_compressed_ids(to_sort, sizes)
ngroups = len(obs_ids)
indexer = _algos.groupsort_indexer(comp_index, ngroups)[0]
indexer = _ensure_platform_int(indexer)
self.sorted_values = algos.take_nd(self.values, indexer, axis=0)
self.sorted_labels = [l.take(indexer) for l in to_sort]
def _make_selectors(self):
new_levels = self.new_index_levels
# make the mask
remaining_labels = self.sorted_labels[:-1]
level_sizes = [len(x) for x in new_levels]
comp_index, obs_ids = get_compressed_ids(remaining_labels, level_sizes)
ngroups = len(obs_ids)
comp_index = _ensure_platform_int(comp_index)
stride = self.index.levshape[self.level] + self.lift
self.full_shape = ngroups, stride
selector = self.sorted_labels[-1] + stride * comp_index + self.lift
mask = np.zeros(np.prod(self.full_shape), dtype=bool)
mask.put(selector, True)
if mask.sum() < len(self.index):
raise ValueError('Index contains duplicate entries, '
'cannot reshape')
self.group_index = comp_index
self.mask = mask
self.unique_groups = obs_ids
self.compressor = comp_index.searchsorted(np.arange(ngroups))
def get_result(self):
# TODO: find a better way than this masking business
values, value_mask = self.get_new_values()
columns = self.get_new_columns()
index = self.get_new_index()
# filter out missing levels
if values.shape[1] > 0:
col_inds, obs_ids = compress_group_index(self.sorted_labels[-1])
# rare case, level values not observed
if len(obs_ids) < self.full_shape[1]:
inds = (value_mask.sum(0) > 0).nonzero()[0]
values = algos.take_nd(values, inds, axis=1)
columns = columns[inds]
# may need to coerce categoricals here
if self.is_categorical is not None:
categories = self.is_categorical.categories
ordered = self.is_categorical.ordered
values = [Categorical(values[:, i], categories=categories,
ordered=ordered)
for i in range(values.shape[-1])]
return DataFrame(values, index=index, columns=columns)
def get_new_values(self):
values = self.values
# place the values
length, width = self.full_shape
stride = values.shape[1]
result_width = width * stride
result_shape = (length, result_width)
mask = self.mask
mask_all = mask.all()
# we can simply reshape if we don't have a mask
if mask_all and len(values):
new_values = (self.sorted_values
.reshape(length, width, stride)
.swapaxes(1, 2)
.reshape(result_shape)
)
new_mask = np.ones(result_shape, dtype=bool)
return new_values, new_mask
# if our mask is all True, then we can use our existing dtype
if mask_all:
dtype = values.dtype
new_values = np.empty(result_shape, dtype=dtype)
else:
dtype, fill_value = maybe_promote(values.dtype, self.fill_value)
new_values = np.empty(result_shape, dtype=dtype)
new_values.fill(fill_value)
new_mask = np.zeros(result_shape, dtype=bool)
name = np.dtype(dtype).name
sorted_values = self.sorted_values
# we need to convert to a basic dtype
# and possibly coerce an input to our output dtype
# e.g. ints -> floats
if needs_i8_conversion(values):
sorted_values = sorted_values.view('i8')
new_values = new_values.view('i8')
name = 'int64'
elif is_bool_dtype(values):
sorted_values = sorted_values.astype('object')
new_values = new_values.astype('object')
name = 'object'
else:
sorted_values = sorted_values.astype(name, copy=False)
# fill in our values & mask
f = getattr(_reshape, "unstack_{}".format(name))
f(sorted_values,
mask.view('u1'),
stride,
length,
width,
new_values,
new_mask.view('u1'))
# reconstruct dtype if needed
if needs_i8_conversion(values):
new_values = new_values.view(values.dtype)
return new_values, new_mask
def get_new_columns(self):
if self.value_columns is None:
if self.lift == 0:
return self.removed_level
lev = self.removed_level
return lev.insert(0, _get_na_value(lev.dtype.type))
stride = len(self.removed_level) + self.lift
width = len(self.value_columns)
propagator = np.repeat(np.arange(width), stride)
if isinstance(self.value_columns, MultiIndex):
new_levels = self.value_columns.levels + (self.removed_level,)
new_names = self.value_columns.names + (self.removed_name,)
new_labels = [lab.take(propagator)
for lab in self.value_columns.labels]
else:
new_levels = [self.value_columns, self.removed_level]
new_names = [self.value_columns.name, self.removed_name]
new_labels = [propagator]
new_labels.append(np.tile(np.arange(stride) - self.lift, width))
return MultiIndex(levels=new_levels, labels=new_labels,
names=new_names, verify_integrity=False)
def get_new_index(self):
result_labels = [lab.take(self.compressor)
for lab in self.sorted_labels[:-1]]
# construct the new index
if len(self.new_index_levels) == 1:
lev, lab = self.new_index_levels[0], result_labels[0]
if (lab == -1).any():
lev = lev.insert(len(lev), _get_na_value(lev.dtype.type))
return lev.take(lab)
return MultiIndex(levels=self.new_index_levels, labels=result_labels,
names=self.new_index_names, verify_integrity=False)
def _unstack_multiple(data, clocs):
if len(clocs) == 0:
return data
# NOTE: This doesn't deal with hierarchical columns yet
index = data.index
clocs = [index._get_level_number(i) for i in clocs]
rlocs = [i for i in range(index.nlevels) if i not in clocs]
clevels = [index.levels[i] for i in clocs]
clabels = [index.labels[i] for i in clocs]
cnames = [index.names[i] for i in clocs]
rlevels = [index.levels[i] for i in rlocs]
rlabels = [index.labels[i] for i in rlocs]
rnames = [index.names[i] for i in rlocs]
shape = [len(x) for x in clevels]
group_index = get_group_index(clabels, shape, sort=False, xnull=False)
comp_ids, obs_ids = compress_group_index(group_index, sort=False)
recons_labels = decons_obs_group_ids(comp_ids, obs_ids, shape, clabels,
xnull=False)
dummy_index = MultiIndex(levels=rlevels + [obs_ids],
labels=rlabels + [comp_ids],
names=rnames + ['__placeholder__'],
verify_integrity=False)
if isinstance(data, Series):
dummy = data.copy()
dummy.index = dummy_index
unstacked = dummy.unstack('__placeholder__')
new_levels = clevels
new_names = cnames
new_labels = recons_labels
else:
if isinstance(data.columns, MultiIndex):
result = data
for i in range(len(clocs)):
val = clocs[i]
result = result.unstack(val)
clocs = [v if i > v else v - 1 for v in clocs]
return result
dummy = data.copy()
dummy.index = dummy_index
unstacked = dummy.unstack('__placeholder__')
if isinstance(unstacked, Series):
unstcols = unstacked.index
else:
unstcols = unstacked.columns
new_levels = [unstcols.levels[0]] + clevels
new_names = [data.columns.name] + cnames
new_labels = [unstcols.labels[0]]
for rec in recons_labels:
new_labels.append(rec.take(unstcols.labels[-1]))
new_columns = MultiIndex(levels=new_levels, labels=new_labels,
names=new_names, verify_integrity=False)
if isinstance(unstacked, Series):
unstacked.index = new_columns
else:
unstacked.columns = new_columns
return unstacked
def pivot(self, index=None, columns=None, values=None):
"""
See DataFrame.pivot
"""
if values is None:
cols = [columns] if index is None else [index, columns]
append = index is None
indexed = self.set_index(cols, append=append)
return indexed.unstack(columns)
else:
if index is None:
index = self.index
else:
index = self[index]
indexed = Series(self[values].values,
index=MultiIndex.from_arrays([index, self[columns]]))
return indexed.unstack(columns)
def pivot_simple(index, columns, values):
"""
Produce 'pivot' table based on 3 columns of this DataFrame.
Uses unique values from index / columns and fills with values.
Parameters
----------
index : ndarray
Labels to use to make new frame's index
columns : ndarray
Labels to use to make new frame's columns
values : ndarray
Values to use for populating new frame's values
Notes
-----
Obviously, all 3 of the input arguments must have the same length
Returns
-------
DataFrame
See also
--------
DataFrame.pivot_table : generalization of pivot that can handle
duplicate values for one index/column pair
"""
if (len(index) != len(columns)) or (len(columns) != len(values)):
raise AssertionError('Length of index, columns, and values must be the'
' same')
if len(index) == 0:
return DataFrame(index=[])
hindex = MultiIndex.from_arrays([index, columns])
series = Series(values.ravel(), index=hindex)
series = series.sort_index(level=0)
return series.unstack()
def _slow_pivot(index, columns, values):
"""
Produce 'pivot' table based on 3 columns of this DataFrame.
Uses unique values from index / columns and fills with values.
Parameters
----------
index : string or object
Column name to use to make new frame's index
columns : string or object
Column name to use to make new frame's columns
values : string or object
Column name to use for populating new frame's values
Could benefit from some Cython here.
"""
tree = {}
for i, (idx, col) in enumerate(zip(index, columns)):
if col not in tree:
tree[col] = {}
branch = tree[col]
branch[idx] = values[i]
return DataFrame(tree)
def unstack(obj, level, fill_value=None):
if isinstance(level, (tuple, list)):
return _unstack_multiple(obj, level)
if isinstance(obj, DataFrame):
if isinstance(obj.index, MultiIndex):
return _unstack_frame(obj, level, fill_value=fill_value)
else:
return obj.T.stack(dropna=False)
else:
unstacker = _Unstacker(obj.values, obj.index, level=level,
fill_value=fill_value)
return unstacker.get_result()
def _unstack_frame(obj, level, fill_value=None):
from pandas.core.internals import BlockManager, make_block
if obj._is_mixed_type:
unstacker = _Unstacker(np.empty(obj.shape, dtype=bool), # dummy
obj.index, level=level,
value_columns=obj.columns)
new_columns = unstacker.get_new_columns()
new_index = unstacker.get_new_index()
new_axes = [new_columns, new_index]
new_blocks = []
mask_blocks = []
for blk in obj._data.blocks:
blk_items = obj._data.items[blk.mgr_locs.indexer]
bunstacker = _Unstacker(blk.values.T, obj.index, level=level,
value_columns=blk_items,
fill_value=fill_value)
new_items = bunstacker.get_new_columns()
new_placement = new_columns.get_indexer(new_items)
new_values, mask = bunstacker.get_new_values()
mblk = make_block(mask.T, placement=new_placement)
mask_blocks.append(mblk)
newb = make_block(new_values.T, placement=new_placement)
new_blocks.append(newb)
result = DataFrame(BlockManager(new_blocks, new_axes))
mask_frame = DataFrame(BlockManager(mask_blocks, new_axes))
return result.loc[:, mask_frame.sum(0) > 0]
else:
unstacker = _Unstacker(obj.values, obj.index, level=level,
value_columns=obj.columns,
fill_value=fill_value)
return unstacker.get_result()
def stack(frame, level=-1, dropna=True):
"""
Convert DataFrame to Series with multi-level Index. Columns become the
second level of the resulting hierarchical index
Returns
-------
stacked : Series
"""
def factorize(index):
if index.is_unique:
return index, np.arange(len(index))
codes, categories = _factorize_from_iterable(index)
return categories, codes
N, K = frame.shape
if isinstance(frame.columns, MultiIndex):
if frame.columns._reference_duplicate_name(level):
msg = ("Ambiguous reference to {0}. The column "
"names are not unique.".format(level))
raise ValueError(msg)
# Will also convert negative level numbers and check if out of bounds.
level_num = frame.columns._get_level_number(level)
if isinstance(frame.columns, MultiIndex):
return _stack_multi_columns(frame, level_num=level_num, dropna=dropna)
elif isinstance(frame.index, MultiIndex):
new_levels = list(frame.index.levels)
new_labels = [lab.repeat(K) for lab in frame.index.labels]
clev, clab = factorize(frame.columns)
new_levels.append(clev)
new_labels.append(np.tile(clab, N).ravel())
new_names = list(frame.index.names)
new_names.append(frame.columns.name)
new_index = MultiIndex(levels=new_levels, labels=new_labels,
names=new_names, verify_integrity=False)
else:
levels, (ilab, clab) = zip(*map(factorize, (frame.index,
frame.columns)))
labels = ilab.repeat(K), np.tile(clab, N).ravel()
new_index = MultiIndex(levels=levels, labels=labels,
names=[frame.index.name, frame.columns.name],
verify_integrity=False)
new_values = frame.values.ravel()
if dropna:
mask = notnull(new_values)
new_values = new_values[mask]
new_index = new_index[mask]
return Series(new_values, index=new_index)
def stack_multiple(frame, level, dropna=True):
# If all passed levels match up to column names, no
# ambiguity about what to do
if all(lev in frame.columns.names for lev in level):
result = frame
for lev in level:
result = stack(result, lev, dropna=dropna)
# Otherwise, level numbers may change as each successive level is stacked
elif all(isinstance(lev, int) for lev in level):
# As each stack is done, the level numbers decrease, so we need
# to account for that when level is a sequence of ints
result = frame
# _get_level_number() checks level numbers are in range and converts
# negative numbers to positive
level = [frame.columns._get_level_number(lev) for lev in level]
# Can't iterate directly through level as we might need to change
# values as we go
for index in range(len(level)):
lev = level[index]
result = stack(result, lev, dropna=dropna)
# Decrement all level numbers greater than current, as these
# have now shifted down by one
updated_level = []
for other in level:
if other > lev:
updated_level.append(other - 1)
else:
updated_level.append(other)
level = updated_level
else:
raise ValueError("level should contain all level names or all level "
"numbers, not a mixture of the two.")
return result
def _stack_multi_columns(frame, level_num=-1, dropna=True):
def _convert_level_number(level_num, columns):
"""
Logic for converting the level number to something we can safely pass
to swaplevel:
We generally want to convert the level number into a level name, except
when columns do not have names, in which case we must leave as a level
number
"""
if level_num in columns.names:
return columns.names[level_num]
else:
if columns.names[level_num] is None:
return level_num
else:
return columns.names[level_num]
this = frame.copy()
# this makes life much simpler
if level_num != frame.columns.nlevels - 1:
# roll levels to put selected level at end
roll_columns = this.columns
for i in range(level_num, frame.columns.nlevels - 1):
# Need to check if the ints conflict with level names
lev1 = _convert_level_number(i, roll_columns)
lev2 = _convert_level_number(i + 1, roll_columns)
roll_columns = roll_columns.swaplevel(lev1, lev2)
this.columns = roll_columns
if not this.columns.is_lexsorted():
# Workaround the edge case where 0 is one of the column names,
# which interferes with trying to sort based on the first
# level
level_to_sort = _convert_level_number(0, this.columns)
this = this.sort_index(level=level_to_sort, axis=1)
# tuple list excluding level for grouping columns
if len(frame.columns.levels) > 2:
tuples = list(zip(*[lev.take(lab)
for lev, lab in zip(this.columns.levels[:-1],
this.columns.labels[:-1])]))
unique_groups = [key for key, _ in itertools.groupby(tuples)]
new_names = this.columns.names[:-1]
new_columns = MultiIndex.from_tuples(unique_groups, names=new_names)
else:
new_columns = unique_groups = this.columns.levels[0]
# time to ravel the values
new_data = {}
level_vals = this.columns.levels[-1]
level_labels = sorted(set(this.columns.labels[-1]))
level_vals_used = level_vals[level_labels]
levsize = len(level_labels)
drop_cols = []
for key in unique_groups:
loc = this.columns.get_loc(key)
# can make more efficient?
# we almost always return a slice
# but if unsorted can get a boolean
# indexer
if not isinstance(loc, slice):
slice_len = len(loc)
else:
slice_len = loc.stop - loc.start
if slice_len == 0:
drop_cols.append(key)
continue
elif slice_len != levsize:
chunk = this.loc[:, this.columns[loc]]
chunk.columns = level_vals.take(chunk.columns.labels[-1])
value_slice = chunk.reindex(columns=level_vals_used).values
else:
if frame._is_mixed_type:
value_slice = this.loc[:, this.columns[loc]].values
else:
value_slice = this.values[:, loc]
new_data[key] = value_slice.ravel()
if len(drop_cols) > 0:
new_columns = new_columns.difference(drop_cols)
N = len(this)
if isinstance(this.index, MultiIndex):
new_levels = list(this.index.levels)
new_names = list(this.index.names)
new_labels = [lab.repeat(levsize) for lab in this.index.labels]
else:
new_levels = [this.index]
new_labels = [np.arange(N).repeat(levsize)]
new_names = [this.index.name] # something better?
new_levels.append(level_vals)
new_labels.append(np.tile(level_labels, N))
new_names.append(frame.columns.names[level_num])
new_index = MultiIndex(levels=new_levels, labels=new_labels,
names=new_names, verify_integrity=False)
result = DataFrame(new_data, index=new_index, columns=new_columns)
# more efficient way to go about this? can do the whole masking biz but
# will only save a small amount of time...
if dropna:
result = result.dropna(axis=0, how='all')
return result
@Appender(_shared_docs['melt'] %
dict(caller='pd.melt(df, ',
versionadded="",
other='DataFrame.melt'))
def melt(frame, id_vars=None, value_vars=None, var_name=None,
value_name='value', col_level=None):
# TODO: what about the existing index?
if id_vars is not None:
if not is_list_like(id_vars):
id_vars = [id_vars]
elif (isinstance(frame.columns, MultiIndex) and
not isinstance(id_vars, list)):
raise ValueError('id_vars must be a list of tuples when columns'
' are a MultiIndex')
else:
id_vars = list(id_vars)
else:
id_vars = []
if value_vars is not None:
if not is_list_like(value_vars):
value_vars = [value_vars]
elif (isinstance(frame.columns, MultiIndex) and
not isinstance(value_vars, list)):
raise ValueError('value_vars must be a list of tuples when'
' columns are a MultiIndex')
else:
value_vars = list(value_vars)
frame = frame.loc[:, id_vars + value_vars]
else:
frame = frame.copy()
if col_level is not None: # allow list or other?
# frame is a copy
frame.columns = frame.columns.get_level_values(col_level)
if var_name is None:
if isinstance(frame.columns, MultiIndex):
if len(frame.columns.names) == len(set(frame.columns.names)):
var_name = frame.columns.names
else:
var_name = ['variable_%s' % i
for i in range(len(frame.columns.names))]
else:
var_name = [frame.columns.name if frame.columns.name is not None
else 'variable']
if isinstance(var_name, compat.string_types):
var_name = [var_name]
N, K = frame.shape
K -= len(id_vars)
mdata = {}
for col in id_vars:
mdata[col] = np.tile(frame.pop(col).values, K)
mcolumns = id_vars + var_name + [value_name]
mdata[value_name] = frame.values.ravel('F')
for i, col in enumerate(var_name):
# asanyarray will keep the columns as an Index
mdata[col] = np.asanyarray(frame.columns
._get_level_values(i)).repeat(N)
return DataFrame(mdata, columns=mcolumns)
def lreshape(data, groups, dropna=True, label=None):
"""
Reshape long-format data to wide. Generalized inverse of DataFrame.pivot
Parameters
----------
data : DataFrame
groups : dict
{new_name : list_of_columns}
dropna : boolean, default True
Examples
--------
>>> import pandas as pd
>>> data = pd.DataFrame({'hr1': [514, 573], 'hr2': [545, 526],
... 'team': ['Red Sox', 'Yankees'],
... 'year1': [2007, 2008], 'year2': [2008, 2008]})
>>> data
hr1 hr2 team year1 year2
0 514 545 Red Sox 2007 2008
1 573 526 Yankees 2007 2008
>>> pd.lreshape(data, {'year': ['year1', 'year2'], 'hr': ['hr1', 'hr2']})
team hr year
0 Red Sox 514 2007
1 Yankees 573 2007
2 Red Sox 545 2008
3 Yankees 526 2008
Returns
-------
reshaped : DataFrame
"""
if isinstance(groups, dict):
keys = list(groups.keys())
values = list(groups.values())
else:
keys, values = zip(*groups)
all_cols = list(set.union(*[set(x) for x in values]))
id_cols = list(data.columns.difference(all_cols))
K = len(values[0])
for seq in values:
if len(seq) != K:
raise ValueError('All column lists must be same length')
mdata = {}
pivot_cols = []
for target, names in zip(keys, values):
to_concat = [data[col].values for col in names]
mdata[target] = _concat._concat_compat(to_concat)
pivot_cols.append(target)
for col in id_cols:
mdata[col] = np.tile(data[col].values, K)
if dropna:
mask = np.ones(len(mdata[pivot_cols[0]]), dtype=bool)
for c in pivot_cols:
mask &= notnull(mdata[c])
if not mask.all():
mdata = dict((k, v[mask]) for k, v in compat.iteritems(mdata))
return DataFrame(mdata, columns=id_cols + pivot_cols)
def wide_to_long(df, stubnames, i, j, sep="", suffix='\d+'):
r"""
Wide panel to long format. Less flexible but more user-friendly than melt.
With stubnames ['A', 'B'], this function expects to find one or more
group of columns with format Asuffix1, Asuffix2,..., Bsuffix1, Bsuffix2,...
You specify what you want to call this suffix in the resulting long format
with `j` (for example `j='year'`)
Each row of these wide variables are assumed to be uniquely identified by
`i` (can be a single column name or a list of column names)
All remaining variables in the data frame are left intact.
Parameters
----------
df : DataFrame
The wide-format DataFrame
stubnames : str or list-like
The stub name(s). The wide format variables are assumed to
start with the stub names.
i : str or list-like
Column(s) to use as id variable(s)
j : str
The name of the subobservation variable. What you wish to name your
suffix in the long format.
sep : str, default ""
A character indicating the separation of the variable names
in the wide format, to be stripped from the names in the long format.
For example, if your column names are A-suffix1, A-suffix2, you
can strip the hypen by specifying `sep='-'`
.. versionadded:: 0.20.0
suffix : str, default '\\d+'
A regular expression capturing the wanted suffixes. '\\d+' captures
numeric suffixes. Suffixes with no numbers could be specified with the
negated character class '\\D+'. You can also further disambiguate
suffixes, for example, if your wide variables are of the form
Aone, Btwo,.., and you have an unrelated column Arating, you can
ignore the last one by specifying `suffix='(!?one|two)'`
.. versionadded:: 0.20.0
Returns
-------
DataFrame
A DataFrame that contains each stub name as a variable, with new index
(i, j)
Examples
--------
>>> import pandas as pd
>>> import numpy as np
>>> np.random.seed(123)
>>> df = pd.DataFrame({"A1970" : {0 : "a", 1 : "b", 2 : "c"},
... "A1980" : {0 : "d", 1 : "e", 2 : "f"},
... "B1970" : {0 : 2.5, 1 : 1.2, 2 : .7},
... "B1980" : {0 : 3.2, 1 : 1.3, 2 : .1},
... "X" : dict(zip(range(3), np.random.randn(3)))
... })
>>> df["id"] = df.index
>>> df
A1970 A1980 B1970 B1980 X id
0 a d 2.5 3.2 -1.085631 0
1 b e 1.2 1.3 0.997345 1
2 c f 0.7 0.1 0.282978 2
>>> pd.wide_to_long(df, ["A", "B"], i="id", j="year")
X A B
id year
0 1970 -1.085631 a 2.5
1 1970 0.997345 b 1.2
2 1970 0.282978 c 0.7
0 1980 -1.085631 d 3.2
1 1980 0.997345 e 1.3
2 1980 0.282978 f 0.1
With multuple id columns
>>> df = pd.DataFrame({
... 'famid': [1, 1, 1, 2, 2, 2, 3, 3, 3],
... 'birth': [1, 2, 3, 1, 2, 3, 1, 2, 3],
... 'ht1': [2.8, 2.9, 2.2, 2, 1.8, 1.9, 2.2, 2.3, 2.1],
... 'ht2': [3.4, 3.8, 2.9, 3.2, 2.8, 2.4, 3.3, 3.4, 2.9]
... })
>>> df
birth famid ht1 ht2
0 1 1 2.8 3.4
1 2 1 2.9 3.8
2 3 1 2.2 2.9
3 1 2 2.0 3.2
4 2 2 1.8 2.8
5 3 2 1.9 2.4
6 1 3 2.2 3.3
7 2 3 2.3 3.4
8 3 3 2.1 2.9
>>> l = pd.wide_to_long(df, stubnames='ht', i=['famid', 'birth'], j='age')
>>> l
ht
famid birth age
1 1 1 2.8
2 3.4
2 1 2.9
2 3.8
3 1 2.2
2 2.9
2 1 1 2.0
2 3.2
2 1 1.8
2 2.8
3 1 1.9
2 2.4
3 1 1 2.2
2 3.3
2 1 2.3
2 3.4
3 1 2.1
2 2.9
Going from long back to wide just takes some creative use of `unstack`
>>> w = l.reset_index().set_index(['famid', 'birth', 'age']).unstack()
>>> w.columns = pd.Index(w.columns).str.join('')
>>> w.reset_index()
famid birth ht1 ht2
0 1 1 2.8 3.4
1 1 2 2.9 3.8
2 1 3 2.2 2.9
3 2 1 2.0 3.2
4 2 2 1.8 2.8
5 2 3 1.9 2.4
6 3 1 2.2 3.3
7 3 2 2.3 3.4
8 3 3 2.1 2.9
Less wieldy column names are also handled
>>> df = pd.DataFrame({'A(quarterly)-2010': np.random.rand(3),
... 'A(quarterly)-2011': np.random.rand(3),
... 'B(quarterly)-2010': np.random.rand(3),
... 'B(quarterly)-2011': np.random.rand(3),
... 'X' : np.random.randint(3, size=3)})
>>> df['id'] = df.index
>>> df
A(quarterly)-2010 A(quarterly)-2011 B(quarterly)-2010 B(quarterly)-2011
0 0.531828 0.724455 0.322959 0.293714
1 0.634401 0.611024 0.361789 0.630976
2 0.849432 0.722443 0.228263 0.092105
\
X id
0 0 0
1 1 1
2 2 2
>>> pd.wide_to_long(df, ['A(quarterly)', 'B(quarterly)'],
i='id', j='year', sep='-')
X A(quarterly) B(quarterly)