Create a new column in multiple dataframes using for loop

Question

I have multiple dataframes with the same structure but different values for instance,

df0, df1, df2...., df9

To each dataframe I want to add a column named eventdate that consists of one date, for instance, 2019-09-15 using for loop

for i in range(0, 9);
    df+str(i)['eventdate'] = "2021-09-15"

but I get an error message SyntaxError: cannot assign to operator

I think it's because df isn't defined. This should be very simple.. Any idea how to do this? thanks.

willwrighteng · Accepted Answer · 2022-11-17 11:15:04Z

1

dfs = [df0, df1, df2...., df9]
dfs_new = []

for i, df in enumerate(dfs):
    df['eventdate'] = "2021-09-15"
    dfs_new.append(df)

if you can't generate a list then you could use eval(f"df{str(num)}") but this method isn't recommended from what I've seen

answered Nov 17, 2022 at 11:15

willwrighteng

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2 Comments

Olive Over a year ago

I do not want to upend dfs.. I just want to have them separate but add a column to each df? in this case, should I just remove the last line of command?

willwrighteng Over a year ago

so then you'll want to use the eval() method. you can assign the df as a tmp variable, add the column, then overwrite the original variable

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