Python: Add value of iteration variable to variable name within for loop

Question

I have a pandas df with a column (let's say col3) containing a number. These numbers are used in multiple rows and I want to run a function for rows of each number separatly.

So I wrote each number once into an array like this:

l = df.col3.unique()

Then a for loop is used to run a function for each number:

for i in l:
   a,b = func(df[df.col3 == i])

So the function gets rows where col3 contains the value of i of each run. The function returns two data frames (a and b in this case). I need these two returned data frames of each run.

I want to be able to identify them properly. For that I would like to save returned data frames within the loop like this:

First run: a123, b123 Second run a456, b456 Third run: a789, b789

Means the name of the dataframe contains the current value of i.

I already read I should not use global variables for dynamic variable names but do not know how to realize this instead.

Thank you :)

I will compare the results. Why is that important? I just want the current value of i within a run to be part of the names of the two data frames. — MaMo
– MaMo, Commented Mar 20, 2018 at 10:17
Why is the name of the variables so important? You can use a dict with the col3's value as the key to save the dataframes. — Lambda
– Lambda, Commented Mar 20, 2018 at 10:48
I need it because if I just call them df1, df2,... then I always need to have a look into them to remember which one contains what data. With the names I would immediatly see which data is in data frame a123. yes, I read about dictonaries but I can't manage to use them properly for my issue. That is why I'm asking this community. — MaMo
– MaMo, Commented Mar 20, 2018 at 14:26

Lambda · Accepted Answer · 2018-03-20 18:22:30Z

1

Solution A (recommended):

dfs = {}

for i in l:
    dfs["a"+str(i)], dfs["b"+str(i)] = func(df[df.col3 == i])
...

And then you can use the dataframes like this:

func2(dfs["a1"]) # dfs["a1"] represents func(df[df.col3 == i])'s first return.
...

Solution B (not recommended)

If you absolutely want to use local variables, you need:

for i in l:
    locals()["a"+str(i)], locals()["b"+str(i)] = func(df[df.col3 == i])

And then you can use the dataframes with their variable names a1,b1 etc.

answered Mar 20, 2018 at 18:22

Lambda

1,3941 gold badge9 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

MaMo Over a year ago

Used your first solution and splitted the list afterwards to have separate dataframes like I need it. Thanks a lot! :)

Collectives™ on Stack Overflow

Python: Add value of iteration variable to variable name within for loop

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related