Setting column equal to value depending on another column pandas

Question

I am stuck on how to set the value of solvent column in each row to a number in the num column in the data frame. eg I need num to be equal to 9 when solvent is Nonane and num equal to 8 when solvent is Octane etc. Any help would be great.

Answer 1

use .loc with a boolean mask

df.loc[df['solvent'] == 'NONANE', 'num'] = 9
df.loc[df['solvent'] == 'OCTANE', 'num'] = 8

Another method is do define a dict and call map:

d = {'NONANE':9, 'OCTANE':8, 'HEPTANE':7, 'HEXANE':6}
df['num'] = df['solvent'].map(d)