Error: The truth value of a Series is ambiguous

user_15508836 0
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I'm trying to generate a new columns using following code

list = ['LHR','-1','-3','LGW','MAD','SIN','KUL','JFK','HKG','PVG','IST','SDA','GLA']
for i in list:
    if plotdata.loc[plotdata['LOCATION'] == i] :
        plotdata['city'] = plotdata['LOCATION']
    else:
        plotdata['city'] = 'others'

I get the following error:

ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

The datatype is category, why do I get this error, please?

pandas series dataframe python
2 Answers

Not sure why you're getting this error. But, it's best-practice to not loop through pandas.

You could avoid that error by setting the "city" to whatever the "location" is and then reverting back to "others" if it's not in the list.

city_list = ['LHR','-1','-3','LGW','MAD','SIN','KUL','JFK','HKG','PVG','IST','SDA','GLA']
plotdata['city'] = plotdata['LOCATION']
plotdata.loc[~plotdata['city'].isin(city_list), 'city'] = 'other'
user_77455060

You get this error because the following code:

if plotdata.loc[plotdata['LOCATION'] == i]

is testing on a subset of the dataframe plotdata returned by .loc(), which in turns is because the Boolean mask:

plotdata['LOCATION'] == i

returns a Boolean array.

Overall, since .loc() returns a subset of dataframe, hence the message:

ValueError: The truth value of a DataFrame is ambiguous.

user_150706970
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