If else condition to compare 2 columns and insert a new column in Python pandas dataframe

Question

I want to compare 2 columns using the following if else condition and update a value in the new column using some formula.

if df.loc[df['TF'] < df['PV']]:
    df['Par_2']] = 0.01*(1.8 * df['PV'] + 32) - 2
elif(some other condition)

While I execute this 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().

Can any one help what can I do to resolve this error. Or is there any other way to compare 2 columns and insert a new column whose value is calculation involving some other columns as shown above.

Answer 1

Use np.where :

df['Par_2']=np.where(df['TF'] < df['PV'], 0.01*(1.8 * df['PV'] + 32) - 2,  'enter here sencond formule')

or numpy.select :

conditions=[df['TF'] < df['PV'],df['TF'] == df['PV'],df['TF'] > df['PV']] #for example
values=[0.01*(1.8 * df['PV'] + 32) - 2, 7, 10] #for example
df['Par_2']=np.select(conditions,values)