[R] Reshape or Stack? (To produce output as columns)

[hadley wickham]

On Tue, Jun 17, 2008 at 5:59 AM, Steve Murray <smurray444 at hotmail.com> wrote:
>
> Dear all,
>
> I have used 'read.table' to create a data frame of 720 columns and 360 rows (and assigned this to 'Jan'). The row and column names are numeric:
>
>> columnnames <- sprintf("%.2f", seq(from = -179.75, to = 179.75, length = 720)).
>> rnames <- sprintf("%.2f", seq(from = -89.75, to = 89.75, length = 360))
>> colnames(Jan) <- columnnames
>> rownames(Jan) <- rnames
>
> A sample of the data looks like this:
>
>> head(Jan)
>       -179.75 -179.25 -178.75 -178.25 -177.75 -177.25 -176.75 -176.25 -175.75
> -89.75   -56.9   -64.2    56.2   -90.0    56.9   -29.0   -91.0   34.0     -9.1
> -89.25    37.9    19.3     -0.4   -12.3   -11.8   -92.1     9.2   -23.5     -0.2
> -88.75    47.4      3.1   -47.4    46.4    34.2      6.1   -41.3    44.7   -10.3
> -88.25   -20.3    34.5   -67.3   -99.9    37.9     -9.3    17.7   -17.2    63.4
> -87.75   -46.4    47.4    12.4   -48.3      9.3   -33.8    38.1    10.8   -34.1
> -87.25   -48.4    10.3   -89.3   -33.0     -1.1   -33.1    81.2    -8.3   -47.2
>
>
> I'm hoping to get the whole dataset into the form of columns, so that, for example, the first row (as shown above) would look like this:
>
> Latitude   Longitude   Value
> -89.75      -179.75     -56.9
> -89.75      -179.25     -64.2
> -89.75      -178.75      56.2
> -89.75      -178.25     -90.0
> -89.75      -177.75      56.9
> -89.75      -177.25     -29.0
> -89.75      -176.75     -91.0
> -89.75      -176.25      34.0
> -89.75      -175.75      -9.1
>
>
> As you can see, this would require the repeated printing of the the row and column names (in this case '-89.75') - so it's not just a case of rearranging the data, but creating 'more' data too.
>
> I've tried to achieve this using 'reshape' and 'stack' (their help files and after looking through the mailing archives), but I'm obviously doing something wrong. For reshape, I'm getting errors relating to the commands I enter, and for stack, I can only produce two columns from my data (with the additional 3rd column being a row count). In any case, these two columns refer to the wrong values (it's producing output in the form of: row count number, Longitude, Value).

This is pretty easy with the reshape package:

install.packages("reshape")
library(reshape)
jan_long <- melt(Jan)

You can find out more at http://had.co.nz/reshape

Hadley

-- 
http://had.co.nz/