Pandas Creating multiple data frames using for loop

Question

I am looking for efficient Python codes to:

1. Create multiple data frames 2. Loop over the multiple data frames

For instance, in my code:

os.chdir(EU_path)
csv_files = glob.glob(EU_path + '\*.csv')
list_EU_data = []
for filename in csv_files:
    data = pd.read_csv(filename)
    list_EU_data.append(data)

list_EU_data is a list of 10 csv files of product sales from 10 European countries. For instance, list_EU_data[0] returns a data frame with columns related to sales information.

Here, I want to create multiple data frames while pre-processing data frames, for instance,

First select columns

EU[0] = list_EU_data[0].iloc[:, [0, 1]]
EU[1] = list_EU_data[1].iloc[:, [0, 1]]
...continues...
EU[9] = list_EU_data[9].iloc[:, [0, 1]]

Next, from each of the data frames, I want to replace 0 values by 1 and iterate all the data frames:

EU[0].iloc[:, 1] = EU[0].iloc[:, 1].replace(0, 1)
EU[1].iloc[:, 1] = EU[1].iloc[:, 1].replace(0, 1)
...continues...
EU[9].iloc[:, 1] = EU[9].iloc[:, 1].replace(0, 1)

Using for loop, what's the most efficient ways to write the above code?

what is code for 1. Create multiple data frames ?

jezrael
– jezrael

2020-11-16 07:24:31 +00:00
Commented Nov 16, 2020 at 7:24 — jezrael
– jezrael, Commented Nov 16, 2020 at 7:24
I've updated code in my post to show data files

JasonSimilar
– JasonSimilar

2020-11-16 09:35:36 +00:00
Commented Nov 16, 2020 at 9:35 — JasonSimilar
– JasonSimilar, Commented Nov 16, 2020 at 9:35

jezrael · Accepted Answer · 2020-11-16 09:37:15Z

1

If need loop solution working with list of DataFrames:

for i, df1 in enumerate(EU):
    df1 = df1.iloc[:, [0, 1]]
    df1.iloc[:, 1] = df1.iloc[:, 1].replace(0, 1)
    EU[i] = df1

Also is possible change your code:

os.chdir(EU_path)
csv_files = glob.glob(EU_path + '\*.csv')
list_EU_data = []
for filename in csv_files:
    data = pd.read_csv(filename)
    data = data.iloc[:, [0, 1]]
    data.iloc[:, 1] = data.iloc[:, 1].replace(0, 1)
    list_EU_data.append(data)

edited Nov 16, 2020 at 9:37

answered Nov 16, 2020 at 7:28

jezrael

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3 Comments

JasonSimilar Over a year ago

In your first chunk of code, 'AttributeError: 'list' object has no attribute 'iloc'

jezrael Over a year ago

@SuhwanChung - Here df is not list, but DataFrame before split.

jezrael Over a year ago

@SuhwanChung - now understand better, what need, so answer was edited.

MonishRajan · Accepted Answer · 2020-11-16 07:56:17Z

0

Please refer my comment on: https://stackoverflow.com/a/64798278/9967586 for creating multiple data frames and looping over those dfs

answered Nov 16, 2020 at 7:56

MonishRajan

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