Iterate over key/value pair from a list()

Question

I'd like to know how I can iterate over a key/value pair from a list object in R, like the example below:

toto <- list(a="my name is",b="I'm called",c="name:") myfun <- function(key,value) paste(value,key) for( key in names(toto) ) toto[key] <- myfun(key,toto[[key]]) 

Is there a way to avoid the for loop (using lapply() or such). Would it be faster?

Thanks!

Answer 1

The best solution of all is to simply call paste directly without a loop (it's vectorized already):

> paste(toto, names(toto)) [1] "my name is a" "I'm called b" "name: c"   

A similar question previously asked on R-Help, with several creative solutions. lapply cannot show the names within the function. This function was provided by Romain Francois based on something by Thomas Lumley:

yapply <- function(X,FUN, ...) {    index <- seq(length.out=length(X))    namesX <- names(X)    if(is.null(namesX))      namesX <- rep(NA,length(X))    FUN <- match.fun(FUN)    fnames <- names(formals(FUN))    if( ! "INDEX" %in% fnames ){      formals(FUN) <- append( formals(FUN), alist(INDEX=) )      }    if( ! "NAMES" %in% fnames ){      formals(FUN) <- append( formals(FUN), alist(NAMES=) )      }    mapply(FUN,X,INDEX=index, NAMES=namesX,MoreArgs=list(...))  } 

Here's an example of usage:

> yapply(toto, function( x ) paste(x, NAMES) )              a              b              c  "my name is a" "I'm called b"      "name: c"