R help - Oct 2014 - how to loop through dataframe objects in environment

Dear All,

I  have many 50 objects they are all dataframes. Each dataframe has many rows
and four column. I simply want to do an addition of 3rd and 4th column and save
the result into 5th column. Since there are many dataframes, I don't want to
do it one by one,  is there a way to loop through all objects and perform the
similar action ?

One way I can think of is like this:

for (i in 1:50){
get(ls()[i])[,3]+get(ls()[i][,4]
}

But I don't know how to save the addition result back to 5th column of each
dataframe.


Many Thanks!



Stephen HK Wong

Hi Stephen,

Try out lapply(). It would help you loop through all data frames and sum.

Regards,
Vikash

On Thu, Oct 16, 2014 at 1:58 AM, Stephen HK Wong <honkit at stanford.edu>
wrote:
> Dear All,
>
> I  have many 50 objects they are all dataframes. Each dataframe has many
> rows and four column. I simply want to do an addition of 3rd and 4th column
> and save the result into 5th column. Since there are many dataframes, I
> don't want to do it one by one,  is there a way to loop through all
objects
> and perform the similar action ?
>
> One way I can think of is like this:
>
> for (i in 1:50){
> get(ls()[i])[,3]+get(ls()[i][,4]
> }
>
> But I don't know how to save the addition result back to 5th column of
> each dataframe.
>
>
> Many Thanks!
>
>
>
> Stephen HK Wong
>
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