I want to know which is the best way to update one element in df based on the value of another coulmn in the same dataframe?

p1["price Now"] = df_emptyex["Close"][i]

Above is the code I use to update the colum, but every row got the same value under column "price Now".

And the result will be:

I want the program to find which row has Company = ASSA-B.ST and update price Now to 200 only on that row like table below:

CodePudding user response：

Use loc:

df.loc[df['Company'] == 'ASSA-B.ST', 'price Now'] = 200

# Before
>>> df
     Company   price Now    Value
0    ALFA.ST  192.421814  915.41:
1  ASSA-B.ST  192.421814   987.81

# After
>>> df
     Company   price Now    Value
0    ALFA.ST  192.421814  915.41:
1  ASSA-B.ST  200.000000   987.81

For more information, you can read the Selection by label section on Indexing and selecting data chapter of the user guide.