[R] Assigning into each of a list of dataframes

[Gabor Grothendieck]

The problem is that your function is returning x$Y rather than x so
the result is a list of Y's rather than a list of the x's with Y added.
You want function(x) { x$Y <- x$A * x$B; x } or a bit shorter:

   lapply(mylist, transform, Y = A * B)


On Jan 18, 2008 10:37 AM, Chuck Cleland <ccleland at optonline.net> wrote:
>   What is the right way to assign a new variable into each a of list of
> data frames?  Here is my failed attempt:
>
> mylist <- list(df1 = data.frame(A = runif(5), B = runif(5)),
>                df2 = data.frame(A = runif(5), B= runif(5)))
>
> lapply(mylist, function(x){x$Y <- x$A * x$B})
>
> $df1
> [1] 0.25589928 0.03446026 0.94992362 0.21388326 0.08668821
>
> $df2
> [1] 0.08771839 0.05643553 0.09036894 0.09179378 0.37394748
>
> mylist
> $df1
>           A          B
> 1 0.3293760 0.77692140
> 2 0.1283307 0.26852710
> 3 0.9865388 0.96288517
> 4 0.5087024 0.42044870
> 5 0.9175345 0.09447951
>
> $df2
>           A         B
> 1 0.3887178 0.2256608
> 2 0.2642189 0.2135938
> 3 0.3881635 0.2328115
> 4 0.9060760 0.1013091
> 5 0.4578424 0.8167602
>
>   I want the variable Y to be added to each data frame in mylist.
>
> thanks,
>
> Chuck
>
> --
> Chuck Cleland, Ph.D.
> NDRI, Inc.
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>
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