Python Question
Replace values in a pandas column that satisfy some condition leads to SettingWithCopyWarning
Let
dtrain<class 'pandas.core.frame.DataFrame'>What is the right way to do the following?
target = dtrain.iloc[:,1] > 0
dtrain.ix[target, 1] = 0
I get the warning:
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pandas/core/indexing.py:477:
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
Note:
Earlier I create
dtraindtrain = d.loc[(d.yyyy < 2005) & (d.yyyy >= 1995),:]
This might be a n00b question. I'm reasonably new to Python and don't have a good model in my head yet of what triggers a deep copy and what's just a pointer...
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Answer Source
I think first can simplify code from:
dtrain = d.loc[(d.yyyy < 2005) & (d.yyyy >= 1995),:]
to:
dtrain = d[(d.yyyy < 2005) & (d.yyyy >= 1995)]
it is called boolean indexing.
dtrain = d[(d.yyyy < 2005) & (d.yyyy >= 1995)].copy()
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