On Oct 4, 2015, at 11:31 AM, FERNANDO MANSITO CABALLERO wrote:
> Dear Madam/Sir,
>
> I am trying to understand R and I have come to a stumbling block. i
> have written:
>
>> Empl <- list(employee="Anna",family=list(spouse="Fred",children=3,
> +child.ages=c(4,7,9)),employee="John",family=list(spouse="Mary",children=2,
> +child.ages=c(14,17)))
>> $family$spouse
> [1] "Fred"
>> #instead of [1] "Fred" "Mary"
>
> Where am I wrong?
The $ function is short-hand for "[[" (with an unevaluated argument). The "[["
function is not able to deliver multiple values. You might think you needed to
use:
sapply( Empl[c(2,4)], function(x){ x$family$spouse )
And you cannot use that construction or its equivalent, because sapply and
lapply do not pass the names of their arguments:
> sapply( Empl[c(2,4)], function(x){ x[['family']]['spouse']} )
$family
NULL
$family
NULL
#-----------
This succeeds:
> sapply( Empl[grepl('family', names(Empl)) ], function(x){x$spouse})
family family
"Fred" "Mary"
--
David Winsemius
Alameda, CA, USA
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