Provide Python-style "for-else"
that works as
follows: for each element, execute "for" block, if there is break
while executing "for" block, then just stop and ignore the "else"
statement, otherwise run "else" block.
Value
If any FUN
returns anything other than NULL
,
then the function returns the first none NULL
object. If
all x
fed to FUN
return NULL
, then this
function returns ALT_FUN
(if ALT_FUN
is not a function)
or the result of ALT_FUN()
.
Examples
# --------------------------- Basic Usage ------------------------------
# 1. ALT_FUN get executed because FUN returns NULL for all items in x
forelse(
1:10,
function(x){
cat('The input is ', x, end = '\n')
if( x > 10) return(x) else return(NULL)
},
function(){
cat('ALT_FUN is executed!\n')
'wow'
}
)
#> The input is 1
#> The input is 2
#> The input is 3
#> The input is 4
#> The input is 5
#> The input is 6
#> The input is 7
#> The input is 8
#> The input is 9
#> The input is 10
#> ALT_FUN is executed!
#> [1] "wow"
# 2. FUN returns non-NULL object
forelse(
1:10,
function(x){
cat('The input is ', x, end = '\n')
if( x %% 2 == 0 ) return(x) else return(NULL)
},
'wow'
)
#> The input is 1
#> The input is 2
#> [1] 2
# --------------------------- Performance ------------------------------
FUN <- function(x){
Sys.sleep(0.01)
if( x %% 2 == 0 ) return(x) else return(NULL)
}
microbenchmark::microbenchmark({
forelse(1:10, FUN, 'wow')
}, {
y <- unlist(lapply(1:10, FUN))
if(length(y)){
y <- y[[1]]
}else{
y <- 'wow'
}
}, {
y <- NULL
for(x in 1:10){ y <- FUN(x) }
if(is.null(y)){ y <- 'wow' }
}, times = 3)
#> Unit: milliseconds
#> expr
#> { forelse(1:10, FUN, "wow") }
#> { y <- unlist(lapply(1:10, FUN)) if (length(y)) { y <- y[[1]] } else { y <- "wow" } }
#> { y <- NULL for (x in 1:10) { y <- FUN(x) } if (is.null(y)) { y <- "wow" } }
#> min lq mean median uq max neval
#> 20.19202 20.19651 20.22116 20.20099 20.23573 20.27046 3
#> 100.77138 100.94835 101.01285 101.12532 101.13359 101.14186 3
#> 100.73431 100.90176 100.95814 101.06921 101.07006 101.07090 3