How to define a function in a for loop with the string parameter using python

Question

Here is a DateFrame,like this:

    df_12=df[df.index.year==2012]

I want to get a series df_X ,X='13','14','15',like bellow

    df_13,df_14...

In fact,I can get it directly,by doing:

   df_13=df[df.index.year==2013]
   df_14=df[df.index.year==2014]
   df_15=df[df.index.year==2015]
   df_16=df[df.index.year==2016]

But ,it will get crazy when the X get very large.So,I try to use a for loop,

  for x in ['13','14','15','16']:
      df_+x=df[df.index.year==int('20'+x)]

It raises a error,and I know why I was wrong. Could anybody get it by using a loop? Thanks!

Are you sure it's == and not =? I'm not familiar with pandas dataframes. Also, I'm surprised that df_+x=... works, as that seems to be assigning to an expression rather than to a reference. Again, I'm not familiar with pandas. — TigerhawkT3
– TigerhawkT3, Commented May 5, 2016 at 7:33
Please post your error message, otherwise we can only guess ;) That said I am guessing that @TigerhawkT3 is right, but I am also not familiar with pandas. — m00am
– m00am, Commented May 5, 2016 at 7:36
Actually, going from df_13, df_14... to df_+x looks like an attempt at variable variables. — TigerhawkT3
– TigerhawkT3, Commented May 5, 2016 at 7:37
You should read this great post by Ned Batchelder. The gist of it is that if writing them all out is going to get overly cumbersome when using a large X, then working with all those variables will also get really cumbersome. You should make a list of dataframes instead. — mgilson
– mgilson, Commented May 5, 2016 at 7:53

Cristiana Panzeri · Accepted Answer · 2016-05-05 08:14:56Z

1

I am not an expert, but I think you coud use dictionaries, and do something like this:

import numpy as np
x=range(10)

name=[0]*len(x)
for i, number in enumerate(x):
    name[i]='df_{0}'.format(x[i])

year=range(2013,2023)

data=dict(zip(name,year))

So, you can recall youd data:

data['df_0']
Out[45]: 2013

Actually, I don't know if you can use it with DataFrames...

answered May 5, 2016 at 8:14

Cristiana Panzeri

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Comments

nigel222 · Accepted Answer · 2016-05-05 08:30:48Z

0

Your problem is that you can't have a variable variable name: df_+x on the left-hand side of an assignment.

@mgilson is right, you should really create a list or dict of date frames. If repeated references to df[df.index.year==2012] is too cumbersome,

df_ = {}
for x in ['13','14','15','16']:
      df_[x]=df[df.index.year==int('20'+x)]

# usage
df_['13']

Integer keys would be less bother to type than string ones, i.e. use for x in [13,14,15,16] and df_[13]

If you are really absolutely determined to do something horrible, there is locals() which gives you access to the local namespace as a dict.

 locals()["df_"+x] = df[df.index.year==int('20'+x)]

My advice: just don't!

answered May 5, 2016 at 8:30

nigel222

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1 Comment

xiao_dong Over a year ago

Thank you for all your help ,I will follow the advices,using df_['13'] type .Thank you all agin :)

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