[R] debug on lapply

[jim holtman]

Typically when I am debugging an 'lapply', I put a browser call inside
the lapply function that is being called and then make sure I 'source'
in the code instead of copy/paste -- the copy/paste will use any
trailing statements after the lapply call as commands to the "browser"
function.

Here is the modified code I used:

lapply( 1:3, function( x ){
    browser()
    x + 1
    }
  )



Here is the output from the console after "sourcing" in the statements above:

> source('clipboard')
Called from: FUN(1:3[[1L]], ...)
Browse[1]> ls()
[1] "x"
Browse[1]> x
[1] 1
Browse[1]> n
debug at clipboard#3: x + 1
Browse[2]> x
[1] 1
Browse[2]> n
Called from: FUN(1:3[[2L]], ...)
Browse[1]> x
[1] 2
Browse[1]> n
debug at clipboard#3: x + 1
Browse[2]>
Called from: FUN(1:3[[3L]], ...)
Browse[1]> n
debug at clipboard#3: x + 1
Browse[2]> x
[1] 3
Browse[2]> n
>


On Tue, Dec 11, 2012 at 1:17 PM, Asis Hallab <asis.hallab at gmail.com> wrote:
> Dear R experts,
>
> recently I tried to debug a R function with an internal lapply call.
> When debugging I seem not to be able to use the "n" command to debug the
> inner function called by lapply.
> How could I achieve this?
>
> *For example:*
> test <- function( ) {
>   lapply( 1:3, function( x ) x + 1 )
> }
> debug( test )
>
> *Start debug:*
>> test()
> debugging in: test()
> debug bei #1:{
>     lapply(1:10, function(x) x + 1)
> }
> Browse[2]> n
> debug bei #2:lapply(1:10, function(x) x + 1)
>
> *The next "n" does not allow me to inspect the inner function,*
> *but gives me the result directly:*
> Browse[2]> n
> exiting from: test()
> [[1]]
> [1] 2
>
> [[2]]
> [1] 3
>
> [[3]]
> [1] 4
>
> Can anyone help me, please?
> Kind regards!
>
>         [[alternative HTML version deleted]]
>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.