CODEWITHSUNDEEP
pythonpandas
Rajeeva I
Rajeeva I

Reputation: 13

I assign list of values to a new column and getting the warning SettingWithCopyWarning:

I have a data frame that has the month and date for 2015. I calculate the Year to Date value into a list. I assign this list to a new column in the data frame but get a warning SettingWithCopyWarning. How do I get around it and some explanation why is this happening. Thanking you all in advance.

print(dfabovemax.head())
print(dfabovemax.tail())
      MaxTemp  Data_Value
Mon-Date                     
01-02         114         113
01-10         142         126
04-10         213         203
04-15         246         228
05-03         203         195
      MaxTemp  Data_Value
Mon-Date                     
01-02         114         113
01-10         142         126
04-10         213         203
04-15         246         228
05-03         203         195

fmt = '%Y-%m-%d'
ytodt2 = []

for i in dfabovemax.index:
    s='2005-{}'.format(i)
    dt = datetime.datetime.strptime(s, fmt)
    tt = dt.timetuple()
    ytodt2.append(tt.tm_yday)

dfabovemax['YtoDt'] = list(ytodt2)

And I get a warning

/opt/conda/lib/python3.6/site-packages/ipykernel/main.py:14: SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame. Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy

print(dfabovemax.head())
print(dfabovemax.tail())

     MaxTemp  Data_Value  YtoDt
Mon-Date                            
01-02         114         113      2
01-10         142         126     10
04-10         213         203    100
04-15         246         228    105
05-03         203         195    123
      MaxTemp  Data_Value  YtoDt
Mon-Date                            
12-25         140         135    359
12-26         152         130    360
12-27         138         118    361
12-28         134         124    362

12-30 134 128 364

Upvotes: 1

Views: 300

Answers (1)

run-out
run-out

Reputation: 3184

You get this warning often when trying to set values on a copy of a dataframe. The only place in your code where this could happen is 

dfabovemax['YtoDt'] = list(ytodt2)

This means that in all likelihood, dfabovemax is the result of another dataframe. In python, the dfabovemax is still referencing the original dataframe that it was made from. In order to rectify this use copy() when you made dfabovemax.

Upvotes: 0

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