There were several interesting points about `ifelse`. The usual behaviour seems
to be that all three inputs are evaluated, and the entries of `yes`
corresponding to `TRUE` in `test` are combined with the entries of `no`
corresponding to `FALSE` in `test`. Moreover, `yes` & `no` seem to be recycled
as necessary in case `test` is longer. On top of that, there seems to be some
sugar that suppresses evaluations in case `all(test)` and/or `all(!test)`, and
the return type can be `logical` even if `yes` & `no` are not. I agreed with
the other responses already, but my experiments further confirmed that `ifelse`
is not interchangeable with `if(....) .... else ....`.
The documentation confirms most of this, but 'same length and attributes
(including dimensions and �"class"�) as �test�' looks wrong. The output seems
to be `logical` or something related to the classes of `yes` & `no`.
Regards,
Jorgen Harmse.
> ifelse(FALSE, {cat("Evaluating the vector for 'if'.\n"); 1:3},
> {cat("Evaluating the vector for 'else'.\n"); 0:4})
Evaluating the vector for 'else'.
[1] 0
> ifelse(rep(FALSE,5L), {cat("Evaluating the vector for 'if'.\n"); 1:3},
> {cat("Evaluating the vector for 'else'.\n"); 0:4})
Evaluating the vector for 'else'.
[1] 0 1 2 3 4
> ifelse(rep(TRUE,3L), {cat("Evaluating the vector for 'if'.\n"); 1:3},
> {cat("Evaluating the vector for 'else'.\n"); 0:4})
Evaluating the vector for 'if'.
[1] 1 2 3
> ifelse(c(TRUE,TRUE,FALSE), {cat("Evaluating the vector for 'if'.\n"); 1:3},
> {cat("Evaluating the vector for 'else'.\n"); 0:4})
Evaluating the vector for 'if'.
Evaluating the vector for 'else'.
[1] 1 2 2
> ifelse(c(TRUE,TRUE,FALSE,TRUE), {cat("Evaluating the vector for 'if'.\n");
> 1:3}, {cat("Evaluating the vector for 'else'.\n"); 0:4})
Evaluating the vector for 'if'.
Evaluating the vector for 'else'.
[1] 1 2 2 1
> args(ifelse)
function (test, yes, no)
NULL
> ifelse(c(TRUE,TRUE,FALSE,TRUE,TRUE,FALSE,TRUE), {cat("Evaluating the vector
> for 'if'.\n"); 1:3}, {cat("Evaluating the vector for 'else'.\n"); 0:4})
Evaluating the vector for 'if'.
Evaluating the vector for 'else'.
[1] 1 2 2 1 2 0 1
> ifelse(logical(0L), {cat("Evaluating the vector for 'if'.\n"); 1:3},
> {cat("Evaluating the vector for 'else'.\n"); 0:4})
logical(0)
> ifelse(TRUE, integer(0L), numeric(0L))
[1] NA
> class(ifelse(TRUE, integer(0L), numeric(0L)))
[1] "integer"
> ifelse(integer(0L)) # test is an empty vector of integers and yes & no are
> missing.
logical(0)
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