Python get data from columns based on condition

Question

Given a dataframe I want to check whether DS1.ColA or DS1.ColB contains "Type 1" and if it does, I want to insert the corresponding DS1.Val to column Value. The same goes for DS2, check if DS2.ColA or DS2.ColB contains "Type 1" and if it does, I want to insert the corresponding DS2.Val to column Value.

df = pd.DataFrame(
{
        'ID': ['AB01', 'AB02', 'AB03', 'AB04', 'AB05','AB06'],
        'DS1.ColA': ["Type 1","Undef",np.nan,"Undef",
                 "Type 1", ""],
        'DS1.ColB': ["N","Type 1","","",
                 "Y", np.nan],
        'DS1.Val': [85,87,18,94,
                 81, 54],
        'DS2.ColA': ["Type 1","Undef","Type 1","Undef",
                 "Type 1", ""],
        'DS2.ColB': ["N","Type 2","","",
                 "Y", "Type 1"],
        'DS2.Val': [45,98,1,45,66,36]
}
)

var_check = "Type 1"
ds1_col_check = ["DS1.ColA","DS1.ColB","DS1.Val"]
ds2_col_check = ["DS2.ColA","DS2.ColB","DS2.Val"]

The last element of ds1_col_check and ds2_col_check is always the element to place in the new column(There could be more columns to checks in the list).The end result df should look like this. How do I achieve this in python?

What is this last column Value indicates in the desired output? — Hetal Thaker
– Hetal Thaker, Commented Oct 11, 2021 at 4:53
It is from DS1.Val or DS2.Val, if DS1 columns has the desired string Value is obtained from DS1.Val else if DS2 columns has the desired string Value is obtained from DS2.Val — Fazli
– Fazli, Commented Oct 11, 2021 at 4:55
And in desired output why is there's a row for AB04 as no column DS1.ColA, DS1.ColB, DS2.ColA, DS2.ColB have "type1" ? — Hetal Thaker
– Hetal Thaker, Commented Oct 11, 2021 at 4:57
There might be cases where "Type 1" is not presented in any of the columns in both DS1 and DS2, so it's nan in value — Fazli
– Fazli, Commented Oct 11, 2021 at 5:02

jezrael · Accepted Answer · 2021-10-11 05:31:09Z

If there is multiple lists is possible create list L and for each sublist test if match condition and set value to column Value, for avoid overwrite values is use Series.fillna:

var_check = "Type 1"
ds1_col_check = ["DS1.ColA","DS1.ColB","DS1.Val"]
ds2_col_check = ["DS2.ColA","DS2.ColB","DS2.Val"]

L = [ds1_col_check, ds2_col_check]

df['Value'] = np.nan
for val in L:
    df.loc[df[val[:-1]].eq(var_check).any(axis=1), 'Value'] = df['Value'].fillna(df[val[-1]])
    
print (df)
     ID DS1.ColA DS1.ColB  DS1.Val DS2.ColA DS2.ColB  DS2.Val  Value
0  AB01   Type 1        N       85   Type 1        N       45   85.0
1  AB02    Undef   Type 1       87    Undef   Type 2       98   87.0
2  AB03      NaN                18   Type 1                 1    1.0
3  AB04    Undef                94    Undef                45    NaN
4  AB05   Type 1        Y       81   Type 1        Y       66   81.0
5  AB06               NaN       54            Type 1       36   36.0

Or:

var_check = "Type 1"
ds1_col_check = ["DS1.ColA","DS1.ColB","DS1.Val"]
ds2_col_check = ["DS2.ColA","DS2.ColB","DS2.Val"]

df.loc[df[ds1_col_check[:-1]].eq(var_check).any(axis=1), 'Value'] = df[ds1_col_check[-1]]
df.loc[df[ds2_col_check[:-1]].eq(var_check).any(axis=1), 'Value'] = df['Value'].fillna(df[ds2_col_check[-1]])

sammywemmy · Accepted Answer · 2021-10-11 06:30:15Z

pyjanitor has a case_when implementation in dev that could be helpful in this case, to abstract multiple conditions (under the hood, it uses pd.Series.mask):

# pip install git+https://github.com/pyjanitor-devs/pyjanitor.git
import pandas as pd
import janitor as jn

 # it has a syntax of 
# condition, value, 
# condition, value, 
# more condition, value pairing, 
# default if none of the conditions match
# column name to assign values to
# similar to a case when in SQL
 df.case_when(
      df['DS1.ColA'].str.contains('Type 1') | df['DS1.ColB'].str.contains('Type 1'), df['DS1.Val'],
      df['DS2.ColA'].str.contains('Type 1') | df['DS2.ColB'].str.contains('Type 1'), df['DS2.Val'],
      np.nan,
      column_name = 'Value')

     ID DS1.ColA DS1.ColB  DS1.Val DS2.ColA DS2.ColB  DS2.Val  Value
0  AB01   Type 1        N       85   Type 1        N       45   85.0
1  AB02    Undef   Type 1       87    Undef   Type 2       98   87.0
2  AB03      NaN                18   Type 1                 1    1.0
3  AB04    Undef                94    Undef                45    NaN
4  AB05   Type 1        Y       81   Type 1        Y       66   81.0
5  AB06               NaN       54            Type 1       36   36.0

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