I want to make a column of a data frame of pandas, the second row to the last row equal to another column's first row to the second last row: it look like:
r(t-1).iloc[1:] = r(t).iloc[0:-1](r(t) and r(t-1))
are columns of the same data frame
the problem I met is python wouldn't get my idea that I want to shift of row of copying data :
IR['r(t-1)'].iloc[1:] = IR['r(t)'].iloc[0:-1]
/anaconda3/lib/python3.6/site-packages/pandas/core/indexing.py:190:
SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame
See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
self._setitem_with_indexer(indexer, value)
any one know how to deal with it?
Welcome to SO.
It seems you need a shift in one of your columns. as the first two lines of your question indicate. you can do it by shift() method for pandas dataframes. Then your answer could possibly would be:
df['new_row'] = df['old_row'].shift(1)
You can shift forward or backward with negative and positive values of shifting
Briefly speaking, pandas has provided ways of data frame writing and reading, and it does not actually accept any other kind of doing that. The warning shows that you are not using a good way (in pandas humble opinion!) of writing to the dataframe (using iloc) as iloc is mostly used for accessing to rows by index.
Any pandas expert here, please correct me if I am wrong.