[R] define variables from a matrix

[Dennis Murphy]

There may well be more efficient ways to do this, but here's one attempt:

foo <- function(x, val) if(any(x == val, na.rm = TRUE)) which(x == val) else NA
u <- apply(A, 1, function(x) foo(x, 20L))
v <- apply(A, 1, function(x) foo(x, 100L))
ifelse(u < v, v, NA)
[1]  3  5 NA NA NA

HTH,
Dennis

On Fri, Aug 12, 2011 at 7:18 PM, gallon li <gallon.li at gmail.com> wrote:
> I have a following matrix and wish to define a variable based the variable
>
>  A=matrix(0,5,5)
> A[1,]=c(30,20,100,120,90)
> A[2,]=c(40,30,20,50,100)
> A[3,]=c(50,50,40,30,30)
> A[4,]=c(30,20,40,50,50)
> A[5,]=c(30,50,NA,NA,100)
>> A
>     [,1] [,2] [,3] [,4] [,5]
> [1,]   30   20  100  120   90
> [2,]   40   30   20   50  100
> [3,]   50   50   40   30   30
> [4,]   30   20   40   50   50
> [5,]   30   50   NA   NA  100
>
> I want to define two variables:
>
> X is the first column in each row that is equal to 20, for example, for the
> first row, I need X=2; 2nd row, X=3; 3rd row, X=NA; 4th row, X=2, 5th row,
> X=NA;
>
> Y is then the first column in each row that is equal to 100 if before this a
> 20 has been reached, for example, for the first row, Y=3; 2nd row, Y=5; 3rd
> row, Y=NA, 4th row, Y=NA; 5th row, Y=NA.
>
> the matrix may involve NA as well.
>
> How can I define these two variables quickly?
>
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