8 messages · John Janmaat, Marc Schwartz, Ott Toomet +4 more
Hello All, Is there a fast way to find the index(row and column) of a point in a matrix? Thanks, John.
-------------------------------------------------------------------------- Dr. John Janmaat Department of Economics, Acadia University, Wolfville, NS, B4P 2R6 E-mail: jjanmaat at acadiau.ca Web: http://ace.acadiau.ca/~jjanmaat Tel: 902-585-1461 Fax: 902-585-1070
-----Original Message----- From: r-help-bounces at stat.math.ethz.ch [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of John Janmaat Sent: Wednesday, April 02, 2003 12:39 PM To: r-help at stat.math.ethz.ch Subject: [R] Index of item in matrix Hello All, Is there a fast way to find the index(row and column) of a point in a
matrix? Thanks, John.
Look at ?which. Specifically the form: which(x, arr.ind = TRUE)
m <- matrix(1:12,3,4) m
[,1] [,2] [,3] [,4] [1,] 1 4 7 10 [2,] 2 5 8 11 [3,] 3 6 9 12
which(m == 9, arr.ind = TRUE)
row col [1,] 3 3
m[3,3]
[1] 9 HTH, Marc Schwartz
Satisfying what conditions?
Does the following example help you get what you want?
> set.seed(1)
> A <- array(rnorm(12), dim=c(3,4))
>
> sel <- (round(A)==1)
> sel
[,1] [,2] [,3] [,4]
[1,] FALSE FALSE FALSE TRUE
[2,] FALSE TRUE FALSE FALSE
[3,] FALSE FALSE FALSE FALSE
> cbind(row(A)[sel],col(A)[sel])
[,1] [,2]
[1,] 2 2
[2,] 1 4
Spencer Graves
Hello All, Is there a fast way to find the index(row and column) of a point in a matrix? Thanks, John.
Hi, | Date: Wed, 02 Apr 2003 14:39:05 -0400 | From: John Janmaat <john.janmaat at acadiau.ca> | Hello All, | | Is there a fast way to find the index(row and column) of a point in a | matrix? what do you mean as ,,a point in a matrix''? Perhaps which( ,arr.ind=T) does what you are looking for. Best wishes, Ott
Hello All, Is there a fast way to find the index(row and column) of a point in a matrix?
x <- matrix(rnorm(25), 5, 5) which(x < -1, arr.ind=TRUE)
row col [1,] 1 1 [2,] 2 1 [3,] 2 2 [4,] 5 2 [5,] 1 3 [6,] 2 4
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Breiviksveien 40, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93 e-mail: Roger.Bivand at nhh.no
Hello All, Is there a fast way to find the index(row and column) of a point in a matrix?
R> a <- matrix(1:25, ncol=5)
R> which(a == 2, arr.ind=TRUE)
row col
[1,] 2 1
R> a
[,1] [,2] [,3] [,4] [,5]
[1,] 1 6 11 16 21
[2,] 2 7 12 17 22
[3,] 3 8 13 18 23
[4,] 4 9 14 19 24
[5,] 5 10 15 20 25
best,
Torsten
Thanks, John. -- -------------------------------------------------------------------------- Dr. John Janmaat Department of Economics, Acadia University, Wolfville, NS, B4P 2R6 E-mail: jjanmaat at acadiau.ca Web: http://ace.acadiau.ca/~jjanmaat Tel: 902-585-1461 Fax: 902-585-1070
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Or more simply:
> set.seed(1)
> A <- array(rnorm(12), dim=c(3,4))
> which(round(A) == 1, arr.ind = TRUE)
row col
[1,] 2 2
[2,] 1 4
Though, the original post may need more clarification.
Sundar
Satisfying what conditions? Does the following example help you get what you want?
> set.seed(1) > A <- array(rnorm(12), dim=c(3,4)) > > sel <- (round(A)==1) > sel
[,1] [,2] [,3] [,4] [1,] FALSE FALSE FALSE TRUE [2,] FALSE TRUE FALSE FALSE [3,] FALSE FALSE FALSE FALSE
> cbind(row(A)[sel],col(A)[sel])
[,1] [,2] [1,] 2 2 [2,] 1 4 Spencer Graves John Janmaat wrote:
Hello All, Is there a fast way to find the index(row and column) of a point in a matrix? Thanks, John.
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Sundar's solution is better than mine unless the code must also work in S-Plus. Spencer Graves
Or more simply:
> set.seed(1) > A <- array(rnorm(12), dim=c(3,4)) > which(round(A) == 1, arr.ind = TRUE)
row col [1,] 2 2 [2,] 1 4 Though, the original post may need more clarification. Sundar Spencer Graves wrote:
Satisfying what conditions? Does the following example help you get what you want?
> set.seed(1) > A <- array(rnorm(12), dim=c(3,4)) > > sel <- (round(A)==1) > sel
[,1] [,2] [,3] [,4] [1,] FALSE FALSE FALSE TRUE [2,] FALSE TRUE FALSE FALSE [3,] FALSE FALSE FALSE FALSE
> cbind(row(A)[sel],col(A)[sel])
[,1] [,2] [1,] 2 2 [2,] 1 4 Spencer Graves John Janmaat wrote:
Hello All, Is there a fast way to find the index(row and column) of a point in a matrix? Thanks, John.
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