/
melt.py
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melt.py
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# pylint: disable=E1101,E1103
# pylint: disable=W0703,W0622,W0613,W0201
import numpy as np
from pandas.core.dtypes.common import is_list_like
from pandas import compat
from pandas.core.arrays import Categorical
from pandas.core.dtypes.generic import ABCMultiIndex
from pandas.core.frame import _shared_docs
from pandas.util._decorators import Appender
import re
from pandas.core.dtypes.missing import notna
from pandas.core.dtypes.common import is_extension_type
from pandas.core.tools.numeric import to_numeric
from pandas.core.reshape.concat import concat
@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, ABCMultiIndex) 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, ABCMultiIndex) 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, ABCMultiIndex):
if len(frame.columns.names) == len(set(frame.columns.names)):
var_name = frame.columns.names
else:
var_name = ['variable_{i}'.format(i=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:
id_data = frame.pop(col)
if is_extension_type(id_data):
id_data = concat([id_data] * K, ignore_index=True)
else:
id_data = np.tile(id_data.values, K)
mdata[col] = id_data
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 frame._constructor(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, 2007], '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 year hr
0 Red Sox 2007 514
1 Yankees 2007 573
2 Red Sox 2008 545
3 Yankees 2008 526
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]
import pandas.core.dtypes.concat as _concat
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 &= notna(mdata[c])
if not mask.all():
mdata = {k: v[mask] for k, v in compat.iteritems(mdata)}
return data._constructor(mdata, columns=id_cols + pivot_cols)
def wide_to_long(df, stubnames, i, j, sep="", suffix=r'\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 hyphen 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
.. versionchanged:: 0.23.0
When all suffixes are numeric, they are cast to int64/float64.
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")
... # doctest: +NORMALIZE_WHITESPACE
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
... # doctest: +NORMALIZE_WHITESPACE
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.unstack()
>>> w.columns = w.columns.map('{0[0]}{0[1]}'.format)
>>> 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
>>> np.random.seed(0)
>>> 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 # doctest: +NORMALIZE_WHITESPACE, +ELLIPSIS
A(quarterly)-2010 A(quarterly)-2011 B(quarterly)-2010 ...
0 0.548814 0.544883 0.437587 ...
1 0.715189 0.423655 0.891773 ...
2 0.602763 0.645894 0.963663 ...
X id
0 0 0
1 1 1
2 1 2
>>> pd.wide_to_long(df, ['A(quarterly)', 'B(quarterly)'], i='id',
... j='year', sep='-')
... # doctest: +NORMALIZE_WHITESPACE
X A(quarterly) B(quarterly)
id year
0 2010 0 0.548814 0.437587
1 2010 1 0.715189 0.891773
2 2010 1 0.602763 0.963663
0 2011 0 0.544883 0.383442
1 2011 1 0.423655 0.791725
2 2011 1 0.645894 0.528895
If we have many columns, we could also use a regex to find our
stubnames and pass that list on to wide_to_long
>>> stubnames = sorted(
... set([match[0] for match in df.columns.str.findall(
... r'[A-B]\(.*\)').values if match != [] ])
... )
>>> list(stubnames)
['A(quarterly)', 'B(quarterly)']
All of the above examples have integers as suffixes. It is possible to
have non-integers as suffixes.
>>> df = pd.DataFrame({
... 'famid': [1, 1, 1, 2, 2, 2, 3, 3, 3],
... 'birth': [1, 2, 3, 1, 2, 3, 1, 2, 3],
... 'ht_one': [2.8, 2.9, 2.2, 2, 1.8, 1.9, 2.2, 2.3, 2.1],
... 'ht_two': [3.4, 3.8, 2.9, 3.2, 2.8, 2.4, 3.3, 3.4, 2.9]
... })
>>> df
birth famid ht_one ht_two
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',
sep='_', suffix='\w')
>>> l
... # doctest: +NORMALIZE_WHITESPACE
ht
famid birth age
1 1 one 2.8
two 3.4
2 one 2.9
two 3.8
3 one 2.2
two 2.9
2 1 one 2.0
two 3.2
2 one 1.8
two 2.8
3 one 1.9
two 2.4
3 1 one 2.2
two 3.3
2 one 2.3
two 3.4
3 one 2.1
two 2.9
Notes
-----
All extra variables are left untouched. This simply uses
`pandas.melt` under the hood, but is hard-coded to "do the right thing"
in a typical case.
"""
def get_var_names(df, stub, sep, suffix):
regex = r'^{stub}{sep}{suffix}$'.format(
stub=re.escape(stub), sep=re.escape(sep), suffix=suffix)
pattern = re.compile(regex)
return [col for col in df.columns if pattern.match(col)]
def melt_stub(df, stub, i, j, value_vars, sep):
newdf = melt(df, id_vars=i, value_vars=value_vars,
value_name=stub.rstrip(sep), var_name=j)
newdf[j] = Categorical(newdf[j])
newdf[j] = newdf[j].str.replace(re.escape(stub + sep), "")
# GH17627 Cast numerics suffixes to int/float
newdf[j] = to_numeric(newdf[j], errors='ignore')
return newdf.set_index(i + [j])
if any(col in stubnames for col in df.columns):
raise ValueError("stubname can't be identical to a column name")
if not is_list_like(stubnames):
stubnames = [stubnames]
else:
stubnames = list(stubnames)
if not is_list_like(i):
i = [i]
else:
i = list(i)
if df[i].duplicated().any():
raise ValueError("the id variables need to uniquely identify each row")
value_vars = [get_var_names(df, stub, sep, suffix) for stub in stubnames]
value_vars_flattened = [e for sublist in value_vars for e in sublist]
id_vars = list(set(df.columns.tolist()).difference(value_vars_flattened))
melted = []
for s, v in zip(stubnames, value_vars):
melted.append(melt_stub(df, s, i, j, v, sep))
melted = melted[0].join(melted[1:], how='outer')
if len(i) == 1:
new = df[id_vars].set_index(i).join(melted)
return new
new = df[id_vars].merge(melted.reset_index(), on=i).set_index(i + [j])
return new