# [R] Filter a big matrix

jim holtman jholtman at gmail.com
Wed Feb 11 14:35:39 CET 2009

```Try something like this.  This setups the "<" condition and then uses
'xor' to flip it to ">=" assuming that you are using the same values

# test data
n <- 5  # number of columns
m <- 100  # number of rows
x <- matrix(sample(1:10, n * m, TRUE), ncol=n, nrow=m)
# create tests assuming you want to know if things are greater than or
less than a value
test <- apply(x, 2, "<", 5)
# setup all combinations to test for
comb <- expand.grid(rep(list(c(TRUE, FALSE)), n))
result <- lapply(seq(nrow(comb)), function(.row){
# apply the test using 'xor' to change the conditions from "<" to ">="
x[apply(test, 1, function(z) all(xor(z, comb[.row,]))),,drop=FALSE]
})

On Wed, Feb 11, 2009 at 7:32 AM, cruz <cruadam at gmail.com> wrote:
> Hi,
>
> I have a big matrix X with M rows and N columns that I want to filter
> it into smaller ones with m (<M) rows and N columns.
> The filter rule is based on the values of each columns, i.e.
>
> X looks like this:
> column name: a, b, c, d, ... etc
>
> a   b   c   d   ...
> 1   2   3   4   ...
> 5   6   7   8   ...
> 9   8   7   6   ...
> ...   ...   ...   ...
>
> The filter rule with the result that I want is:
>
> X[X\$a<5 & X\$b<5 & X\$c<5 & X\$d<5 ...etc ,]
> X[X\$a<5 & X\$b<5 & X\$c<5 & X\$d>=5 ...etc ,]
> X[X\$a<5 & X\$b<5 & X\$c>=5 & X\$d<5 ...etc ,]
> ...   ...   ...
> ...
>
> with all the possible combinations which is 2^M
>
> I try to use multiple for loops to separate it:
>
> for (i in 1:2)
>  for (j in 1:2)
>    for (k in 1:2)
>      ... ...
>        assign(paste(i,j,k,...,sep="")), X[if (i==1) paste("X\$a<5")
> else paste("X\$a>=5") & if (i==1) paste("X\$b<5") else paste("X\$b>=5") &
> ..., ])
>
> # there might be syntax errors, I just want to clearly describe my problem
>
> Since paste("X\$a>=5") gives type of character; whereas the type of
> X\$a>=5 should be logical.
>
> How can I do this?
>
> All thoughts are greatly appreciated.
>
> Many Thanks,
> cruz
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

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