R help - Feb 2006 - unused factor levels in reshape

When reshaping a dataframe in which there are unused factor levels in the id
variable, I get the following error:

Error in if (!all(really.constant)) warning(gettextf("some constant
variables (%s) are really varying",  :
        missing value where TRUE/FALSE needed

For example,
> df <- data.frame(i = factor(rep(1:5, each = 2)), t = factor(rep(1:2,
5)), x = rep(rbinom(5, 1, 0.5), each = 2), y = rpois(10, 10))
> subdf <- subset(df, i %in% 1:3)
defines a dataframe, and a subframe with some unused factor levels (i = 4, 5).
Then
> reshape(df, v.names = "y", timevar = "t", idvar =
"i", direction = "wide")
  i x y.1 y.2
1 1 0  13   6
3 2 0  12   5
5 3 0  10   9
7 4 1   9  11
9 5 1  12   8

works fine but
> reshape(subdf, v.names = "y", timevar = "t", idvar =
"i", direction = "wide")
Error in if (!all(really.constant)) warning(gettextf("some constant
variables (%s) are really varying",  :
        missing value where TRUE/FALSE needed

produces the error, which happens during the check to see if the variables
assumed constant are constant. The problem is that reshape searches over all the
levels of the id variable (i in this case) to see if the other variables (here
x) are constant. But there is no x associated with i = 4, 5 in the smaller
dataframe, so
> tapply(subdf$x, subdf$i, function(x) length(unique(x)) == 1)
   1    2    3    4    5 
TRUE TRUE TRUE   NA   NA

produces some NAs. A slight change to the reshape code to work around this
problem would be to use (the equivalent of)
> tapply(subdf$x, subdf$i[, drop = TRUE], function(x) length(unique(x)) == 1)
   1    2    3 
TRUE TRUE TRUE

in the reshapeWide function within reshape, but perhaps there is a good reason
not to do this?

Daniel

On Wed, 22 Feb 2006, Daniel Farewell wrote:
> When reshaping a dataframe in which there are unused factor levels in 
> the id variable, I get the following error:
>
> Error in if (!all(really.constant)) warning(gettextf("some constant
variables (%s) are really varying",  :
>        missing value where TRUE/FALSE needed
Yes, I think it's a bug. Thanks for pointing it out.

 	-thomas
>
> For example,
>
>> df <- data.frame(i = factor(rep(1:5, each = 2)), t = factor(rep(1:2,
5)), x = rep(rbinom(5, 1, 0.5), each = 2), y = rpois(10, 10))
>
>> subdf <- subset(df, i %in% 1:3)
>
> defines a dataframe, and a subframe with some unused factor levels (i = 4,
5). Then
>
>> reshape(df, v.names = "y", timevar = "t", idvar =
"i", direction = "wide")
>  i x y.1 y.2
> 1 1 0  13   6
> 3 2 0  12   5
> 5 3 0  10   9
> 7 4 1   9  11
> 9 5 1  12   8
>
> works fine but
>
>> reshape(subdf, v.names = "y", timevar = "t", idvar
= "i", direction = "wide")
> Error in if (!all(really.constant)) warning(gettextf("some constant
variables (%s) are really varying",  :
>        missing value where TRUE/FALSE needed
>
> produces the error, which happens during the check to see if the variables
assumed constant are constant. The problem is that reshape searches over all the
levels of the id variable (i in this case) to see if the other variables (here
x) are constant. But there is no x associated with i = 4, 5 in the smaller
dataframe, so
>
>> tapply(subdf$x, subdf$i, function(x) length(unique(x)) == 1)
>   1    2    3    4    5
> TRUE TRUE TRUE   NA   NA
>
> produces some NAs. A slight change to the reshape code to work around this
problem would be to use (the equivalent of)
>
>> tapply(subdf$x, subdf$i[, drop = TRUE], function(x) length(unique(x))
== 1)
>   1    2    3
> TRUE TRUE TRUE
>
> in the reshapeWide function within reshape, but perhaps there is a good
reason not to do this?
>
> Daniel
>
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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle