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Error -> The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all()

May 30, 2022

Could you please help me sort out the below if condition:
(could be also possible with apply and lambda but don’t know how to put so many conditions in single line)

test = pd.DataFrame({'index' : ['DS','VS','VB','FS','HB'],
   'bid' : [np.nan,102,103,104,np.NaN],
   'mid'  : [106,107,108,109,110],
    'ask' : [np.nan,112,113,114,115]})

print(test)

  index    bid  mid    ask
0    DS    NaN  106    NaN
1    VS  102.0  107  112.0
2    VB  103.0  108  113.0
3    FS  104.0  109  114.0
4    HB    NaN  110  115.0

What I tried :

if (test['index'].str.endswith('B') and test['bid'] > 0).all():
    test['fin'] == test['bid']
elif (test['index'].str.endswith('S')) and (test['ask'] > 0).all():
    test['fin'] == test['ask']
elif test['bid'] > 0:
    test['fin'] == test['bid']
elif test['mid'] > 0:
    test['fin'] == test['mid']
else:
    test['fin'] == test['ask']

Still getting the error message:

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

.Expected output:

  index    bid  mid    ask    fin
0    DS    NaN  106    NaN  106.0   
1    VS  102.0  107  112.0  112.0
2    VB  103.0  108  113.0  103.0
3    FS  104.0  109  114.0  114.0
4    HB    NaN  110  115.0  110.0    110 because no bid

explanation:
I want to a new ‘fin’ columns based on the condition:
if index ends with B and bid > 0 add bid value;
if index end with S and ask > 0 add ask value;
if those 2 conditions fail (ie end with a S but only bid available) if bid > 0 add bid value;
if mid > 0 add mid value;
if ask > 0 add ask value.

>Solution :

When your condition is quite complicated, it might be easier to write the condition in afunction and apply it to every rows by using df.apply(func, axis=1)

import pandas as pd
import numpy as np
test = pd.DataFrame({'index' : ['DS','VS','VB','FS','HB'],
   'bid' : [np.nan,102,103,104,np.NaN],
   'mid'  : [106,107,108,109,110],
    'ask' : [np.nan,112,113,114,115]})


def extract_value(row):
    if row['index'].endswith('B') and row['bid'] > 0:
        return row['bid']
    elif row['index'].endswith('S') and row['ask'] > 0:
        return row['ask']
    elif row['bid'] > 0:
        return row['bid']
    elif row['mid'] > 0:
        return row['mid']
    else:
        return row['ask']


test['fin'] = test.apply(extract_value, axis=1)