You can make make a factor with a common set of levels out of each slice of
the matrix so all the tables are the same size:

f <- function (charMatrix, levels = unique(sort(as.vector(charMatrix))))
{
    apply(charMatrix, 1, function(x) table(factor(x, levels = levels)))
}
used as
> m <- cbind(c("A","A","A"), c("B", "A", "A"))
> f(m)
  [,1] [,2] [,3]
A    1    2    2
B    1    0    0



Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Thu, Jul 10, 2014 at 10:03 AM, Jonathan Greenberg <jgrn@illinois.edu>
wrote:

> R-helpers:
>
> I'm trying to determine the frequency of characters for a matrix
> applied to a single dimension, and generate a matrix as an output.
> I've come up with a solution, but it appears inelegant -- I was
> wondering if there is an easier way to accomplish this task:
>
> # Create a matrix of "factors" (characters):
> random_characters=matrix(sample(letters[1:4],1000,replace=TRUE),100,10)
>
> # Applying with the table() function doesn't work properly, because not
> all rows
> # have ALL of the factors, so I get a list output:
> apply(random_characters,1,table)
>
> # Hacked solution:
> unique_values = letters[1:4]
>
> countsmatrix <- t(apply(random_characters,1,function(x,unique_values)
> {
> counts=vector(length=length(unique_values))
> for(i in seq(unique_values))
> {
> counts[i] = sum(x==unique_values[i])
> }
> return(counts)
> },
> unique_values=unique_values
> ))
>
> # Gets me the output I want but requires two nested loops (apply and
> for() ), so
> # not efficient for very large datasets.
>
> ###
>
> Is there a more elegant solution to this?
>
> --j
>
> --
> Jonathan A. Greenberg, PhD
> Assistant Professor
> Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
> Department of Geography and Geographic Information Science
> University of Illinois at Urbana-Champaign
> 259 Computing Applications Building, MC-150
> 605 East Springfield Avenue
> Champaign, IL  61820-6371
> Phone: 217-300-1924
> http://www.geog.illinois.edu/~jgrn/
> AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307, Skype: jgrn3007
>
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>

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