Dear R users,
I'm having some problems with the stack() and unstack() functions, and
wondered if you could help.
I have a large data frame (400 rows x 2000 columns), which I need to reduce
to a single column of values (and therefore 800000 rows), so that I can use
it in other operations (e.g., generating predictions from a GLM object).
However, the problem I'm having can be reproduced with something as simple
as this:
> testdat <- data.frame("1" = c(1:5), "2" = c(1:5), "10" = c(1:5))
> testdat
X1 X2 X10
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
5 5 5 5
Please note that the numeric column names are what I'm dealing with in my
real data frame too. Stacking into a long format works fine:
> stacked <- stack(testdat)
> stacked
values ind
1 1 X1
2 2 X1
3 3 X1
4 4 X1
5 5 X1
6 1 X2
7 2 X2
8 3 X2
9 4 X2
10 5 X2
11 1 X10
12 2 X10
13 3 X10
14 4 X10
15 5 X10
But the problem I have comes in unstacking, when the order of the columns is
changed from the original, to something alphabetical (i.e. X10 goes before
X2):
> unstacked <- unstack(stacked)
> unstacked
X1 X10 X2
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
5 5 5 5
Maintaining the order of columns is very important for me, as I'm dealing
with spatial data.
Is there a way of modifying the 'form' argument in unstack to maintain
numerical ordering of columns? Or, is there a quick way of re-ordering the
columns in a data frame into a numerical order? Alternatively, is there
another function or package that could do this? I've tried reshape() but it
seems very slow when I use my full data frame with it.
Any help would be very much appreciated,
Many thanks,
Matthew Carroll
--
Matthew Carroll
Department of Biology (Area 18),
University of York,
E-mail: mjc...@york.ac.uk
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