Python Pandas User Warning: Sorting because non-concatenation axis is not aligned

Question

I'm doing some code practice and applying merging of data frames while doing this getting user warning

/usr/lib64/python2.7/site-packages/pandas/core/frame.py:6201: FutureWarning: Sorting because non-concatenation axis is not aligned. A future version of pandas will change to not sort by default. To accept the future behavior, pass 'sort=True'. To retain the current behavior and silence the warning, pass sort=False

On these lines of code: Can you please help to get the solution of this warning.

placement_video = [self.read_sql_vdx_summary, self.read_sql_video_km]
placement_video_summary = reduce(lambda left, right: pd.merge(left, right, on='PLACEMENT', sort=False), placement_video)


placement_by_video = placement_video_summary.loc[:, ["PLACEMENT", "PLACEMENT_NAME", "COST_TYPE", "PRODUCT",
                                                     "VIDEONAME", "VIEW0", "VIEW25", "VIEW50", "VIEW75",
                                                     "VIEW100",
                                                     "ENG0", "ENG25", "ENG50", "ENG75", "ENG100", "DPE0",
                                                     "DPE25",
                                                     "DPE50", "DPE75", "DPE100"]]

# print (placement_by_video)

placement_by_video["Placement# Name"] = placement_by_video[["PLACEMENT",
                                                            "PLACEMENT_NAME"]].apply(lambda x: ".".join(x),
                                                                                     axis=1)

placement_by_video_new = placement_by_video.loc[:,
                         ["PLACEMENT", "Placement# Name", "COST_TYPE", "PRODUCT", "VIDEONAME",
                          "VIEW0", "VIEW25", "VIEW50", "VIEW75", "VIEW100",
                          "ENG0", "ENG25", "ENG50", "ENG75", "ENG100", "DPE0", "DPE25",
                          "DPE50", "DPE75", "DPE100"]]

placement_by_km_video = [placement_by_video_new, self.read_sql_km_for_video]
placement_by_km_video_summary = reduce(lambda left, right: pd.merge(left, right, on=['PLACEMENT', 'PRODUCT'], sort=False),
                                       placement_by_km_video)

#print (list(placement_by_km_video_summary))
#print(placement_by_km_video_summary)
#exit()
# print(placement_by_video_new)
"""Conditions for 25%view"""
mask17 = placement_by_km_video_summary["PRODUCT"].isin(['Display', 'Mobile'])
mask18 = placement_by_km_video_summary["COST_TYPE"].isin(["CPE", "CPM", "CPCV"])
mask19 = placement_by_km_video_summary["PRODUCT"].isin(["InStream"])
mask20 = placement_by_km_video_summary["COST_TYPE"].isin(["CPE", "CPM", "CPE+", "CPCV"])
mask_video_video_completions = placement_by_km_video_summary["COST_TYPE"].isin(["CPCV"])
mask21 = placement_by_km_video_summary["COST_TYPE"].isin(["CPE+"])
mask22 = placement_by_km_video_summary["COST_TYPE"].isin(["CPE", "CPM"])
mask23 = placement_by_km_video_summary["PRODUCT"].isin(['Display', 'Mobile', 'InStream'])
mask24 = placement_by_km_video_summary["COST_TYPE"].isin(["CPE", "CPM", "CPE+"])

choice25video_eng = placement_by_km_video_summary["ENG25"]
choice25video_vwr = placement_by_km_video_summary["VIEW25"]
choice25video_deep = placement_by_km_video_summary["DPE25"]

placement_by_km_video_summary["25_pc_video"] = np.select([mask17 & mask18, mask19 & mask20, mask17 & mask21],
                                                  [choice25video_eng, choice25video_vwr, choice25video_deep])


"""Conditions for 50%view"""
choice50video_eng = placement_by_km_video_summary["ENG50"]
choice50video_vwr = placement_by_km_video_summary["VIEW50"]
choice50video_deep = placement_by_km_video_summary["DPE50"]

placement_by_km_video_summary["50_pc_video"] = np.select([mask17 & mask18, mask19 & mask20, mask17 & mask21],
                                                  [choice50video_eng,
                                                   choice50video_vwr, choice50video_deep])

"""Conditions for 75%view"""

choice75video_eng = placement_by_km_video_summary["ENG75"]
choice75video_vwr = placement_by_km_video_summary["VIEW75"]
choice75video_deep = placement_by_km_video_summary["DPE75"]

placement_by_km_video_summary["75_pc_video"] = np.select([mask17 & mask18, mask19 & mask20, mask17 & mask21],
                                                  [choice75video_eng,
                                                   choice75video_vwr,
                                                   choice75video_deep])

"""Conditions for 100%view"""

choice100video_eng = placement_by_km_video_summary["ENG100"]
choice100video_vwr = placement_by_km_video_summary["VIEW100"]
choice100video_deep = placement_by_km_video_summary["DPE100"]
choicecompletions = placement_by_km_video_summary['COMPLETIONS']

placement_by_km_video_summary["100_pc_video"] = np.select([mask17 & mask22, mask19 & mask24, mask17 & mask21, mask23 & mask_video_video_completions],
                                                          [choice100video_eng, choice100video_vwr, choice100video_deep, choicecompletions])



"""conditions for 0%view"""

choice0video_eng = placement_by_km_video_summary["ENG0"]
choice0video_vwr = placement_by_km_video_summary["VIEW0"]
choice0video_deep = placement_by_km_video_summary["DPE0"]

placement_by_km_video_summary["Views"] = np.select([mask17 & mask18, mask19 & mask20, mask17 & mask21],
                                                   [choice0video_eng,
                                                    choice0video_vwr,
                                                    choice0video_deep])


#print (placement_by_km_video_summary)
#exit()

#final Table

placement_by_video_summary = placement_by_km_video_summary.loc[:,
                             ["PLACEMENT", "Placement# Name", "PRODUCT", "VIDEONAME", "COST_TYPE",
                              "Views", "25_pc_video", "50_pc_video", "75_pc_video","100_pc_video",
                              "ENGAGEMENTS","IMPRESSIONS", "DPEENGAMENTS"]]

#placement_by_km_video = [placement_by_video_summary, self.read_sql_km_for_video]
#placement_by_km_video_summary = reduce(lambda left, right: pd.merge(left, right, on=['PLACEMENT', 'PRODUCT']),
                                       #placement_by_km_video)


#print(placement_by_video_summary)
#exit()
# dup_col =["IMPRESSIONS","ENGAGEMENTS","DPEENGAMENTS"]

# placement_by_video_summary.loc[placement_by_video_summary.duplicated(dup_col),dup_col] = np.nan

# print ("Dhar",placement_by_video_summary)

'''adding views based on conditions'''
#filter maximum value from videos

placement_by_video_summary_new = placement_by_km_video_summary.loc[
    placement_by_km_video_summary.reset_index().groupby(['PLACEMENT', 'PRODUCT'])['Views'].idxmax()]
#print (placement_by_video_summary_new)
#exit()
# print (placement_by_video_summary_new)
# mask22 = (placement_by_video_summary_new.PRODUCT.str.upper ()=='DISPLAY') & (placement_by_video_summary_new.COST_TYPE=='CPE')

placement_by_video_summary_new.loc[mask17 & mask18, 'Views'] = placement_by_video_summary_new['ENGAGEMENTS']
placement_by_video_summary_new.loc[mask19 & mask20, 'Views'] = placement_by_video_summary_new['IMPRESSIONS']
placement_by_video_summary_new.loc[mask17 & mask21, 'Views'] = placement_by_video_summary_new['DPEENGAMENTS']

#print (placement_by_video_summary_new)
#exit()
placement_by_video_summary = placement_by_video_summary.drop(placement_by_video_summary_new.index).append(
    placement_by_video_summary_new).sort_index()

placement_by_video_summary["Video Completion Rate"] = placement_by_video_summary["100_pc_video"] / \
                                                      placement_by_video_summary["Views"]

placement_by_video_final = placement_by_video_summary.loc[:,
                           ["Placement# Name", "PRODUCT", "VIDEONAME", "Views",
                            "25_pc_video", "50_pc_video", "75_pc_video", "100_pc_video",
                            "Video Completion Rate"]]

score 152 · Accepted Answer · edited Oct 29 '19 at 07:58

tl;dr:

concat and append currently sort the non-concatenation index (e.g. columns if you're adding rows) if the columns don't match. In pandas 0.23 this started generating a warning; pass the parameter sort=True to silence it. In the future the default will change to not sort, so it's best to specify either sort=True or False now, or better yet ensure that your non-concatenation indices match.

The warning is new in pandas 0.23.0:

In a future version of pandas pandas.concat() and DataFrame.append() will no longer sort the non-concatenation axis when it is not already aligned. The current behavior is the same as the previous (sorting), but now a warning is issued when sort is not specified and the non-concatenation axis is not aligned, link.

More information from linked very old github issue, comment by smcinerney :

When concat'ing DataFrames, the column names get alphanumerically sorted if there are any differences between them. If they're identical across DataFrames, they don't get sorted.

This sort is undocumented and unwanted. Certainly the default behavior should be no-sort.

After some time the parameter sort was implemented in pandas.concat and DataFrame.append:

sort : boolean, default None

Sort non-concatenation axis if it is not already aligned when join is 'outer'. The current default of sorting is deprecated and will change to not-sorting in a future version of pandas.

Explicitly pass sort=True to silence the warning and sort. Explicitly pass sort=False to silence the warning and not sort.

This has no effect when join='inner', which already preserves the order of the non-concatenation axis.

So if both DataFrames have the same columns in the same order, there is no warning and no sorting:

df1 = pd.DataFrame({"a": [1, 2], "b": [0, 8]}, columns=['a', 'b'])
df2 = pd.DataFrame({"a": [4, 5], "b": [7, 3]}, columns=['a', 'b'])

print (pd.concat([df1, df2]))
   a  b
0  1  0
1  2  8
0  4  7
1  5  3

df1 = pd.DataFrame({"a": [1, 2], "b": [0, 8]}, columns=['b', 'a'])
df2 = pd.DataFrame({"a": [4, 5], "b": [7, 3]}, columns=['b', 'a'])

print (pd.concat([df1, df2]))
   b  a
0  0  1
1  8  2
0  7  4
1  3  5

But if the DataFrames have different columns, or the same columns in a different order, pandas returns a warning if no parameter sort is explicitly set (sort=None is the default value):

df1 = pd.DataFrame({"a": [1, 2], "b": [0, 8]}, columns=['b', 'a'])
df2 = pd.DataFrame({"a": [4, 5], "b": [7, 3]}, columns=['a', 'b'])

print (pd.concat([df1, df2]))

FutureWarning: Sorting because non-concatenation axis is not aligned.

   a  b
0  1  0
1  2  8
0  4  7
1  5  3

print (pd.concat([df1, df2], sort=True))
   a  b
0  1  0
1  2  8
0  4  7
1  5  3

print (pd.concat([df1, df2], sort=False))
   b  a
0  0  1
1  8  2
0  7  4
1  3  5

If the DataFrames have different columns, but the first columns are aligned - they will be correctly assigned to each other (columns a and b from df1 with a and b from df2 in the example below) because they exist in both. For other columns that exist in one but not both DataFrames, missing values are created.

Lastly, if you pass sort=True, columns are sorted alphanumerically. If sort=False and the second DafaFrame has columns that are not in the first, they are appended to the end with no sorting:

df1 = pd.DataFrame({"a": [1, 2], "b": [0, 8], 'e':[5, 0]}, 
                    columns=['b', 'a','e'])
df2 = pd.DataFrame({"a": [4, 5], "b": [7, 3], 'c':[2, 8], 'd':[7, 0]}, 
                    columns=['c','b','a','d'])

print (pd.concat([df1, df2]))

FutureWarning: Sorting because non-concatenation axis is not aligned.

   a  b    c    d    e
0  1  0  NaN  NaN  5.0
1  2  8  NaN  NaN  0.0
0  4  7  2.0  7.0  NaN
1  5  3  8.0  0.0  NaN

print (pd.concat([df1, df2], sort=True))
   a  b    c    d    e
0  1  0  NaN  NaN  5.0
1  2  8  NaN  NaN  0.0
0  4  7  2.0  7.0  NaN
1  5  3  8.0  0.0  NaN

print (pd.concat([df1, df2], sort=False))

   b  a    e    c    d
0  0  1  5.0  NaN  NaN
1  8  2  0.0  NaN  NaN
0  7  4  NaN  2.0  7.0
1  3  5  NaN  8.0  0.0

In your code:

placement_by_video_summary = placement_by_video_summary.drop(placement_by_video_summary_new.index)
                                                       .append(placement_by_video_summary_new, sort=True)
                                                       .sort_index()

I don't quite understand this: `In a future version of pandas pandas.concat() and DataFrame.append() will no longer sort the non-concatenation axis when it is not already aligned. ` what is a `non-concatenation axis` and what the result will look like? does column a and column b will mismatch? or just the column order is different? — an offer can't refuse, Sep 30 '18 at 09:52
It's not clear what `is not aligned` means - could you comment on that? — Mr_and_Mrs_D, Dec 03 '18 at 04:17
I believe `aligned` means that the levels in the axis are the same: if there is a difference of any kind, they are no longer `aligned` and will trigger this behaviour (e.g. if axis levels are `['c','b','a']` and `['a']`) — Robert Muil, Dec 13 '18 at 10:29
@RobertMuil I think using the term `level` here is potentially confusing as `level` has a specific meaning for pandas dataframes when there is a MultiIndex. From what I understand, `aligned` in this context refers to the ordering of the row/column index. So if the non-concatenation axis index order is different for your two frames, then you can specify whether to retain the order in the first frame passed, and sort the second frame to match, or to sort the index of BOTH frames before concatenation. This is a confusing area for me too so corrections welcome! — ac24, Jan 07 '19 at 14:44
Columns are aligned when `tuple(df1.columns) == tuple(df2.columns)`. The non-concatenation axis is the axis (rows or columns) parallel to the seams along which the DataFrames are being stitched together. — BallpointBen, Jan 30 '20 at 23:14
@jezrael i have this error but i don't understand this, how can i fix this please? — Sarindra Thérèse, Jun 03 '21 at 12:11

score 110 · Answer 2 · answered Oct 23 '18 at 21:41

110

jezrael's answer is good, but did not answer a question I had: Will getting the "sort" flag wrong mess up my data in any way? The answer is apparently "no", you are fine either way.

from pandas import DataFrame, concat

a = DataFrame([{'a':1,      'c':2,'d':3      }])
b = DataFrame([{'a':4,'b':5,      'd':6,'e':7}])

>>> concat([a,b],sort=False)
   a    c  d    b    e
0  1  2.0  3  NaN  NaN
0  4  NaN  6  5.0  7.0

>>> concat([a,b],sort=True)
   a    b    c  d    e
0  1  NaN  2.0  3  NaN
0  4  5.0  NaN  6  7.0

answered Oct 23 '18 at 21:41

RLC

1,264
1
8
5

what exactly is hier sorted or not sorted? – Ben Aug 06 '19 at 10:06
3

@Ben the warning appears when the column order is different between dataframes. As you can see if sort=True then the columns after concatentation are sorted alphabetically – MP23 Sep 02 '19 at 18:52
1

In this example it does not, but if you concatenate multiple Series or DataFrames with a DatetimeIndex the rows are no longer in chronological order. Technically the data isn't messed up, but your result might be harder to read. – hugovdberg Oct 23 '19 at 09:59

Python Pandas User Warning: Sorting because non-concatenation axis is not aligned

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