CODEWITHSUNDEEP
pythonpandasdataframeseries
Yi Yu
Yi Yu

Reputation: 33

Error: The truth value of a Series is ambiguous

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?

Upvotes: 3

Views: 631

Answers (2)

SeaBean
SeaBean

Reputation: 23217

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.

Upvotes: 0

Ollie in PGH
Ollie in PGH

Reputation: 2629

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'

Upvotes: 2

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