Accessing list names in lapply

Thanks to everybody who replied - I got three distinct, very useful
suggestions.

Bjarke Christensen



                                                                           
             Romain Francois                                               
             <romain.francois@                                             
             dbmail.com>                                               Til 
                                       Bjarke Christensen                  
             19-11-2009 14:33          <Bjarke.Christensen at sydbank.dk>     
                                                                        cc 
                                       r-help at r-project.org                
                                                                      Emne 
                                       Re: [R] Accessing list names in     
                                       lapply                              
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           




Maybe this : http://tolstoy.newcastle.edu.au/R/e4/help/08/04/8720.html

Romain

Hi,

When using lapply (or sapply) to loop over a list, can I somehow access

the

index of the list from inside the function?

A trivial example:

df1<- split(
    x=rnorm(n=100, sd=seq(from=1, to=10, each=10)),
    f=letters[seq(from=1, to=10, each=10)]
  )
str(df1)
#List of 10
# $ a: num [1:10] -0.801 0.418 1.451 -0.554 -0.578 ...
# $ b: num [1:10] -2.464 0.279 4.099 -2.483 1.921 ...
# $ c: num [1:10] -1.14 -1.773 2.512 -2.072 -0.904 ...
# $ d: num [1:10] 2.109 1.243 0.627 -2.343 -6.071 ...
#...
par(mfcol=c(5,2))
lapply(df1, plot)

This plots each element of the list, but the label on the vertical axis

is

X[[0L]] (as expected from the documentation in ?lapply). I'd like the
heading for each plot to be the name of that item in the list. This can

be

achieved by using a for-loop:

for (i in names(df1)) plot(df1[[i]], ylab=i)

but can it somehow be achieved bu using lapply? I would be hoping for
something like

lapply(df1, function(x) plot(x, ylab=parent.index()))

or some way to parse the index number out of the call, using match.call()
or something like that.

Thanks in advance for any comments,
Bjarke Christensen

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Romain Francois
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