On Aug 12, 2011, at 7:18 PM, gallon li 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;
X <- apply(A, 1, function(x) which(x==20) )
is.na(X) <- !unlist(lapply(X, length))
X
The first command seems obvious, but the second might be a bit
obscure. It says assign NA to any X whose length is non-zero (i.e.
positive in the case of length).
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.
Y <- apply(A, 1, function(x) which(x==20)*(which(x==20) <
which(x==100) ) )
is.na(Y) <- !unlist(lapply(Y, length))
Y
--
David.
the matrix may involve NA as well.
How can I define these two variables quickly?
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
______________________________________________
[email protected] mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
