change a value based on other value in dataframe

Question

If product type == option, I replace the value in the PRICE column with the value of the STRIKE column.

How can I do this without using the for loop? (to make it faster)

Now I have the following but it's slow:

for i in range(df.shape[0]):
   if df.loc[i,'type'] == 'Option:
       df.loc[i,'PRICE'] = df.loc[i,'STRIKE']

please provide the input/output data (or examples) as text – mozway Oct 11 '21 at 19:23 — mozway, Oct 11 '21 at 19:23

score 1 · Accepted Answer · answered Oct 11 '21 at 19:27

1

Use .loc in a vectorized fashion

df.loc[df['type'] == 'Option', 'PRICE'] = df['STRIKE']

answered Oct 11 '21 at 19:27

Corralien

score 0 · Answer 2 · answered Oct 11 '21 at 19:27

0

mask = (df.type == 'Option')
df[mask].PRICE = df[mask].STRIKE

answered Oct 11 '21 at 19:27

honi

`df[mask].PRICE` is not safe because you're not guaranteed that `df[mask]` will return a view and not a copy and so the potential for failure to update exists as if `df[mask]` returns a copy the updated values will not be reflected in `df`. – Henry Ecker Oct 11 '21 at 21:10

2 Answers2