Pandas dataframe: Manipulate column depending on value in another column (without iterating over rows)

Question

Without looping/iterating over rows I would like to manipulate a dataframe so that depending on the value in one column (Transaction_Type) the value in another column (Gross_Value) gets multiplied by -1 or not.

Transaction_#  Transaction_Type  Gross_Value
 5542-6990      Invoice             39.00
 5981-3808      SalesCredit         89.00
 8058-9885      Invoice            199.00
 5420-6262      SalesCredit         99.00 

For all sales credits the Gross_Value should be represented with the negative number:

Transaction_#  Transaction_Type  Gross_Value
 5542-6990      Invoice             39.00
 5981-3808      SalesCredit        -89.00
 8058-9885      Invoice            199.00
 5420-6262      SalesCredit        -99.00 

Thanks!

Answer 1

Use loc

m = (df['Transaction_Type'] == 'SalesCredit')
df.loc[m, 'Gross_Value'] *= -1

---

  Transaction_# Transaction_Type  Gross_Value
0     5542-6990          Invoice         39.0
1     5981-3808      SalesCredit        -89.0
2     8058-9885          Invoice        199.0
3     5420-6262      SalesCredit        -99.0

Answer 2

尝试这个

df.loc[df['Transaction_Type'] == 'Sales Credit','Gross_Value'] = df['Gross_Value'] * -1