[R] table over a matrix dimension...
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: jgrn...@hotmail.com, Gchat: jgrn307, Skype: jgrn3007
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Re: [R] table over a matrix dimension...
On Jul 10, 2014, at 12:03 PM, Jonathan Greenberg j...@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
If I am correctly understanding your issue, you simply need to coerce the input
to table() to a factor with a common set of levels, since the matrix will be
'character' by default:
set.seed(1)
random_characters - matrix(sample(factor(letters[1:4]), 1000, replace = TRUE),
100, 10)
random_characters
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] b c b c c c d d d d
[2,] b b a a a c d d a d
[3,] c b c b d c a d d b
[4,] d d b b d c c c c a
[5,] a c a b d b d c b a
[6,] d a c d c d d a c a
[7,] d a c a b b b b b a
[8,] c b a d d d b c d a
[9,] c d b a a d d d b a
[10,] a c c b d c a c a a
[11,] a d d a d d d c b c
[12,] a c a a b b b b b d
[13,] c b d d c a c a b c
[14,] b b d c d c c d d a
[15,] d a d b c c c b b a
[16,] b a b b b a b b c b
[17,] c c c a b c a a d a
[18,] d a d b b c b a d c
...
RES - t(apply(random_characters, 1,
function(x) table(factor(x, levels = letters[1:4]
RES
a b c d
[1,] 0 2 4 4
[2,] 4 2 1 3
[3,] 1 3 3 3
[4,] 1 2 4 3
[5,] 3 3 2 2
[6,] 3 0 3 4
[7,] 3 5 1 1
[8,] 2 2 2 4
[9,] 3 2 1 4
[10,] 4 1 4 1
[11,] 2 1 2 5
[12,] 3 5 1 1
[13,] 2 2 4 2
[14,] 1 2 3 4
[15,] 2 3 3 2
[16,] 2 7 1 0
[17,] 4 1 4 1
[18,] 2 3 2 3
...
Regards,
Marc Schwartz
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Re: [R] table over a matrix dimension...
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]
A122
B100
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Thu, Jul 10, 2014 at 10:03 AM, Jonathan Greenberg j...@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: jgrn...@hotmail.com, Gchat: jgrn307, Skype: jgrn3007
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
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and provide commented, minimal, self-contained, reproducible code.
