concat multiple dataframe with index as loop variable

Question

I create multiple dataframes by for loop and concat them, which works fine. But I need to include loop variable as index. I cant find a way to set loop variable as index

maindf=pd.DataFrame()
for i in ['20170724','20170725','20170726']:
    a=pd.read_csv("somecsv."+str(i))
    maindf = pd.concat(maindf,a,axis=0)

Expected OP for maindf:

         A  B  C
20170724 1  2  3
         4  5  6
         7  8  9
20170725 11 22 33
         44 55 66
         77 88 99
20170725 111 222 333
         444 555 666
         777 888 999

jezrael · Accepted Answer · 2017-07-26 15:03:16Z

3

I think you need append all DataFrames to list and then use concat with parameter keys, also for remove second level add reset_index with parameter drop:

dfs = []
vals = ['20170724','20170725','20170726']
for i in vals:
    a=pd.read_csv("somecsv."+str(i))
    dfs.append(a)
maindf = pd.concat(dfs,keys=vals).reset_index(level=1, drop=True)

answered Jul 26, 2017 at 15:03

jezrael

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piRSquared · Accepted Answer · 2017-07-26 15:07:17Z

1

You can use pd.concat on a dictionary.

lst = ['20170724','20170725','20170726']
pd.concat({k: pd.read_csv('somecsv.{}'.format(i)) for k in lst})

answered Jul 26, 2017 at 15:07

piRSquared

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