Doran, Harold wrote:
> I have a data set where I want the correlations between 2 variables
> conditional on a students grade level.
>
> This code works just fine.
>
> by(tmp[,c('mtsc07', 'DCBASmathscoreSPRING')], tmp$Grade, cor,
> use='complete', method='pearson')
>
> However, this generates an error
>
> by(tmp[,c('mtsc07', 'DCBASmathscoreSPRING')], tmp$Grade, cor,
> use='complete', method='spearman')
> Error in FUN(data[x, ], ...) : 'x' is empty
>
> I can subset the data by grade and compute spearman rho as
>
> tmp5 <- subset(tmp, Grade == 5)
> cor(tmp5[,c('mtsc07', 'DCBASmathcountSPRING')], use='complete',
> method='spearman')
>
> But doing this iteratively is inefficient.
>
> I don't see anything in the help man for by() or cor() that tells me
> what the problem is. I might be missing it though. Any thoughts?
It works as expected using the iris data:
by(iris[,c('Sepal.Length', 'Sepal.Width')], iris$Species, cor,
use='complete', method='spearman')
iris$Species: setosa
Sepal.Length Sepal.Width
Sepal.Length 1.0000000 0.7553375
Sepal.Width 0.7553375 1.0000000
---------------------------------------------------------------------------------------------------------------------
iris$Species: versicolor
Sepal.Length Sepal.Width
Sepal.Length 1.000000 0.517606
Sepal.Width 0.517606 1.000000
---------------------------------------------------------------------------------------------------------------------
iris$Species: virginica
Sepal.Length Sepal.Width
Sepal.Length 1.0000000 0.4265165
Sepal.Width 0.4265165 1.0000000
> sessionInfo()
R version 2.5.1 Patched (2007-09-16 r42884)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
attached base packages:
[1] "stats" "graphics" "grDevices" "utils" "datasets"
"methods" "base"
other attached packages:
lattice
"0.16-5"
> Thanks,
> Harold
>
>
>> sessionInfo()
> R version 2.5.0 (2007-04-23)
> i386-pc-mingw32
>
> locale:
> LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
> States.1252;LC_MONETARY=English_United
> States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
>
> attached base packages:
> [1] "stats" "graphics" "grDevices" "utils" "datasets"
> "methods" "base"
>
> other attached packages:
> lattice
> "0.15-4"
>
>
> [[alternative HTML version deleted]]
>
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--
Chuck Cleland, Ph.D.
NDRI, Inc.
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