# Re: [R] searching for specific row in matrix

From: Dimitris Rizopoulos <dimitris.rizopoulos_at_med.kuleuven.be>
Date: Wed, 11 Jun 2008 14:52:14 +0200

match.pat <- function (mat, target, nomatch = -1) {

```##################
```

set.seed(1234)
mat <- matrix(sample(0:1, 50, TRUE), 10, 5)

targ1 <- mat[2, ]
match.pat(mat, targ1)

targ2 <- rep(0, 5)
match.pat(mat, targ2)

I hope it helps.

Best,
Dimitris

Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven

```Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
http://www.student.kuleuven.be/~m0390867/dimitris.htm

```
• Original Message ----- From: "Esmail Bonakdarian" <esmail.js_at_gmail.com> To: <r-help_at_r-project.org> Sent: Wednesday, June 11, 2008 1:58 PM Subject: [R] searching for specific row in matrix

> Hi,
>
> I have matrix of bits and a target vector. Is there an
> efficient way to search the rows of the matrix for the target?
> I am interested in the first row index where target is found.
>
> Example:
>
> > source("lookup.R")
> [,1] [,2] [,3] [,4] [,5]
> [1,] 1 0 1 1 0
> [2,] 1 1 0 1 0
> [3,] 0 0 1 0 0
> [4,] 1 0 0 1 1
> [5,] 1 0 1 1 1
> [6,] 1 1 0 0 1
> [7,] 1 0 0 1 1
> [8,] 0 0 1 1 1
> [9,] 0 1 1 0 1
> [10,] 0 0 0 1 0
>
> target: 1 1 0 1 1
>
> Should return -1 (or some other indicator) since the
>
>
>
> > source("lookup.R")
> [,1] [,2] [,3] [,4] [,5]
> [1,] 0 0 1 1 0
> [2,] 1 0 0 0 0
> [3,] 1 0 0 0 0
> [4,] 1 1 0 0 0
> [5,] 1 1 1 0 0
> [6,] 0 0 1 1 0
> [7,] 0 1 1 1 0
> [8,] 0 0 1 1 0
> [9,] 1 1 0 1 1
> [10,] 1 0 1 0 0
>
> target: 1 1 0 1 1
>
> Should return 9 since the target was found in row 9
>
>
> If the target is found, it is no longer necessary to keep
> searching the rest of the matrix (which may be quite large)
>
> The data/size etc may change of course, but target will
> always have the same number of "columns" as the matrix.
>
> I tried variations of "which", and a for loop
> comparing pop[i,] to target without much success, nor
> did google yield any results. I am hoping someone here
> can provide a suggestion.
>
> Thanks,
>
> EB
>
>
> ---------------------------------------------
>
> # Here is the code that generates the above data
>
> create_bin_string <- function(len)
> {
> sample(0:1, len, replace=T)
> }
>
> ROWS = 10
> COLS = 5
> pop = matrix(create_bin_string(ROWS*COLS), ROWS, COLS, byrow=T)
>
>
>
> target=c(1, 1, 0, 1, 1)
>
> # my population
> print(pop)
>
> # I am looking for the index of this in pop
> # if present (else -1?)
> cat("\ntarget: ", target, "\n")
>
>
>
> ##
> ## this is NOT working
> ## plus it would continue to search
> ## after it found the target
> ##
> for(i in ROWS)
> if (pop[i,] == target)
> cat("\nfound in row: ", i, "\n\n")
>
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