Python 3.4 and Pandas 0.15.0
df is a dataframe and col1 is a column. With the code below, I'm checking for the presence of the value 10 and replacing such values with 1000.
df.col1[df.col1 == 10] = 1000
Here's another example. This time, I'm changing values in col2 based on index.
df.col2[df.index == 151] = 500
Both these produce the warning below:
-c:1: SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame See the the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
cols = ['col1', 'col2', 'col3'] df[cols] = df[cols].applymap(some_function)
This produces a similar warning, with an added suggestion:
Try using .loc[row_indexer,col_indexer] = value instead
I'm not sure I understand the discussion pointed to in the warnings. What would be a better way to write these three lines of code?
Note that the operations worked.