R help - May 2024 - Get a copy of a matrix only for TRUE entries of a matching size boolean matrix?

Is there a way to get a copy of a matrix only for TRUE entries of a
matching size boolean matrix? For *example*:
> mat_letters <- matrix(data=c('A', 'B', 'C',
'D'), ncol=2, byrow=TRUE)
> mat_letters
     [,1] [,2]
[1,] "A"  "B"
[2,] "C"  "D"
> mat_bools <- matrix(data=c(FALSE, TRUE, TRUE, FALSE), ncol=2,
byrow=TRUE)
> mat_bools
      [,1]  [,2]
[1,] FALSE  TRUE
[2,]  TRUE FALSE
*Reminder:* The following is only an example ; the solution might look very
different.
some_command(mat_letters, mat_bools, false=empty)
     [,1] [,2]
[1,] ""  "B"
[2,] "C"  ""
some_command(mat_letters, mat_bools, false=na)
     [,1] [,2]
[1,] NA  "B"
[2,] "C"  NA

Thank you kindly

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In two steps:

result <- matrix(NA_character_,
    nrow=nrow(mat_letters), ncol =ncol(mat_letters))
result[mat_bools] <- mat_letters[mat_bools]

On 2024-05-03 8:47 a.m., DynV Montrealer wrote:
> Is there a way to get a copy of a matrix only for TRUE entries of a
> matching size boolean matrix? For *example*:
>> mat_letters <- matrix(data=c('A', 'B', 'C',
'D'), ncol=2, byrow=TRUE)
>> mat_letters
>       [,1] [,2]
> [1,] "A"  "B"
> [2,] "C"  "D"
>> mat_bools <- matrix(data=c(FALSE, TRUE, TRUE, FALSE), ncol=2,
byrow=TRUE)
>> mat_bools
>        [,1]  [,2]
> [1,] FALSE  TRUE
> [2,]  TRUE FALSE
> *Reminder:* The following is only an example ; the solution might look very
> different.
> some_command(mat_letters, mat_bools, false=empty)
>       [,1] [,2]
> [1,] ""  "B"
> [2,] "C"  ""
> some_command(mat_letters, mat_bools, false=na)
>       [,1] [,2]
> [1,] NA  "B"
> [2,] "C"  NA
> 
> Thank you kindly
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
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Is it what you want ?
mat_letters <- matrix(data=c('A', 'B', 'C',
'D'), ncol=2, byrow=TRUE)
mat_bools <- matrix(data=c(FALSE, TRUE, TRUE, FALSE), ncol=2, byrow=TRUE)

ifelse(mat_bools, mat_letters, "")
ifelse(mat_bools, mat_letters, NA)

 > ifelse(mat_bools, mat_letters, "")
 ???? [,1] [,2]
[1,] ""?? "B"
[2,] "C"? ""
 > ifelse(mat_bools, mat_letters, NA)
 ???? [,1] [,2]
[1,] NA?? "B"
[2,] "C"? NA

Marc



Le 03/05/2024 ? 14:47, DynV Montrealer a ?crit?:
> Is there a way to get a copy of a matrix only for TRUE entries of a
> matching size boolean matrix? For*example*:
>> mat_letters <- matrix(data=c('A', 'B', 'C',
'D'), ncol=2, byrow=TRUE)
>> mat_letters
>       [,1] [,2]
> [1,] "A"  "B"
> [2,] "C"  "D"
>> mat_bools <- matrix(data=c(FALSE, TRUE, TRUE, FALSE), ncol=2,
byrow=TRUE)
>> mat_bools
>        [,1]  [,2]
> [1,] FALSE  TRUE
> [2,]  TRUE FALSE
> *Reminder:* The following is only an example ; the solution might look very
> different.
> some_command(mat_letters, mat_bools, false=empty)
>       [,1] [,2]
> [1,] ""  "B"
> [2,] "C"  ""
> some_command(mat_letters, mat_bools, false=na)
>       [,1] [,2]
> [1,] NA  "B"
> [2,] "C"  NA

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