Change column (categorical) value based on another column (float)

Question

I try to execute this code to replace all df_dash['aoh'] <=262 to standby

if df_dash['aoh'] <= 262:
   df_dash['category'] = 'standby'

However I get this error, and I cannot seem to find a way to get the right results.

Traceback (most recent call last): File "<input>", line 1, in <module> File "/Users/jacob/anaconda3/envs/MERS/lib/python3.7/site-packages/pandas/core/generic.py", line 1555, in __nonzero__ self.__class__.__name__ ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

I have read about this error in other threads, but I cannot seem to find a solution to this specific case.

I tried using this as well

df_dash['category'] = np.where(df_dash['aoh'] <= 262, 'standby', df['category'])

But, I get

ValueError: operands could not be broadcast together with shapes (458,) () (4173,)

Hoping someone could help

Possible duplicate of [Conditional Replace Pandas](https://stackoverflow.com/questions/21608228/conditional-replace-pandas) — Michael Gardner, Sep 17 '19 at 23:39

score 0 · Accepted Answer · answered Sep 17 '19 at 23:33

0

 df_dash['category'][df_dash['aoh'] <= 262] = 'standby'

answered Sep 17 '19 at 23:33

Aiden Zhao

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it works perfectly, but don't you think it can be just as good to use loc? @YongkangZhao – ansev Sep 18 '19 at 00:58
loc is better when the df slice is being pass around functions to make sure the data is being passed as reference in case it needs to be modified inplace – Aiden Zhao Sep 18 '19 at 01:00

score 0 · Answer 2 · answered Sep 17 '19 at 23:35

0

You can use loc with boolean indexing:

df_dash.loc[df_dash['aoh'] <= 262,'category'] = 'standby'

answered Sep 17 '19 at 23:35

ansev

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score 0 · Answer 3 · answered Sep 17 '19 at 23:43

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Worth nothing - your np.where solution should have worked, but I think you used df['category'] in the second part of the function call, not df_dash['category'].

Can't see the rest of the code but assume the dataframes are different sizes.

answered Sep 17 '19 at 23:43

elembie

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Change column (categorical) value based on another column (float)

3 Answers3