Dimension Mismatch using melt() in reshape2

Question

I am trying to melt a data frame from 'wide' format to 'long' format in R, using the function 'melt' in the package 'reshape2'. However, I am encountering an issue with dimensions when trying to view the output data frame which I am having trouble deciphering. Here is an example:

# load reshape2 package
require(reshape2)

# sample data frame generated using dput
df <- structure(list(year = c(2001, 2002, 2003, 2004), 
                     aet = structure(c(493.1, 407.1, 476.7, 501.6), .Dim = 4L), 
                     drainage = structure(c(5.4, 5.4, 5.4, 5.4), .Dim = 4L), 
                     srunoff = structure(c(25.6, 24.3, 56.0, 50.3), .Dim = 4L)),
                .Names = c("year", "aet", "drainage", "srunoff"), row.names = c(NA, 4L), class = "data.frame")

# if i melt without specifying id.vars, it provides a warning but works works fine
df.melt <- melt(df)

# check output
head(df.melt)

# view output
View(df.melt)
# this works fine, and the data frame is visible in RStudio

# now, melt while supplying year as an id variable
df.melt.id <- melt(df, id.vars="year")

# check output
head(df.melt.id)
# the first 6 lines of output print to the console menu, as normal

# view output
View(df.melt.id)

However, when I try to view the df.melt.id data frame, I get the following error:

Error in FUN(X[[i]], ...) : 
  dims [product 4] do not match the length of object [12]

4 corresponds to the original length of the data frame, and 12 is how long it should be. If I check the dimensions using dim(df.melt.id), it returns the appropriate size: [1] 12 3

Any ideas on what's going on here? I have tried re-installing reshape2 and that did not help...

If you look at `str(df.melt.id)`, somehow the `value` column became an array. If you coerce it to numeric, it's fine, but the behavior seems pretty buggy. — alistaire, Apr 06 '16 at 20:42
It's a `reshape2` thing; `reshape::melt.data.frame` works fine. — alistaire, Apr 06 '16 at 20:45
Strange! Yes, using `reshape` works fine on both this sample and my original, larger data frame. Thanks for the quick help. — Sam Zipper, Apr 06 '16 at 20:51
You should also [file a bug report](https://github.com/hadley/reshape/issues). — alistaire, Apr 06 '16 at 21:02
The problem is that your original columns in the `data.frame` are arrays (they have a length one `dim` attribute) and those are not properly handled by `reshape2`. I've submitted a PR to fix that. — Kevin Ushey, Apr 06 '16 at 21:32

score 2 · Accepted Answer · 2016-04-06T21:14:18.820

2

It works with reshape2 when you do this:

df.melt.id <- as.data.frame.array(melt(df, id="year"))

edited Apr 06 '16 at 21:14

answered Apr 06 '16 at 21:00

Dimension Mismatch using melt() in reshape2

1 Answers1