Pandas Columns From Another Dataframe If Value Is In Another Column?

I have pd.DataFrame listing wire gauges and their corresponding currents: e_ref = wire_gauge current 0 14 15 1 12 20 2 10 30 3

Solution 1:

Use map by Series created form e_ref or join, but is necessary values in currentcolumn in e_ref has to be unique:

print (e_ref['current'].is_unique)
True

s = e_ref.set_index('current')['wire_gauge']
system['wire_gauge'] = system['breakers'].map(s)
print (system)
   breakers  wire_gauge
0301012012230103151443010

Alternative:

df = system.join(e_ref.set_index('current'), on='breakers')
print (df)
   breakers  wire_gauge
0        30          10
1        20          12
2        30          10
3        15          14
4        30          10