how to change dataframes using a loop in Python Pandas?

Question

I have N dataframes ranging from L1...Ln.

I would like to modify them to keep rows pertaining to a certain condition.

I ran the following loop:

for df in [L1,...,Ln]:
    df=df.ix[df['Sector']=='Services']

However, when I call out each dataframe, I find it has not been replaced accordingly. How do I modify a set of dataframes using a loop?

I am using Python 2.7.

score 2 · Answer 1 · answered Jul 31 '17 at 10:06

2

You need to overwrite the old dataframe with the new one:

all_dfs = [L1,...,Ln]
# iterate through the dataframes one by one
# keep track of the order in index and the content in df 
for index, df in enumerate(all_dfs):
    # modify the current dataframe df 
    # then overwrite the old one in the same index. 
    all_dfs[index]= df.ix[df['Sector']=='Services']

answered Jul 31 '17 at 10:06

Mohamed Ali JAMAOUI

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Am I not doing so currently through df=df...? – runawaykid Jul 31 '17 at 10:11
2

@runawaykid you are overwriting the local variable df. but not the actual df in the list. – Mohamed Ali JAMAOUI Jul 31 '17 at 10:12
I find that I need to add the line [L1,...Ln] = all_dfs at the end for this to work when I call out L1. If not its still the original dataframe. – runawaykid Jul 31 '17 at 10:17
@runawaykid of course, because all_dfs is a copy of [L1,...Ln]. In anycase, you have to assign your list [L1,...Ln] to a variable and use the variable instead of the list.. – Mohamed Ali JAMAOUI Jul 31 '17 at 10:24

how to change dataframes using a loop in Python Pandas?

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