Mon, 2005-06-06 at 16:54 -0700, Jeff D. Hamann wrote:
r-gurus,

I couldn't find an answer to this and after an hour or so of trying all
types or ways to do this, I've given up for now.

I'm having trouble getting the results from xtabs to generate
"unsorted" factors. I've generated a sample data.frame I want to
create a table from, using xtabs, and the results are presented below,

temp
treatment itpa qmd tht
1 0 100 7.287263 3.362501
2 25 100 10.461070 4.118217
3 50 100 16.671731 5.814391
4 75 100 24.033238 8.264608
5 100 100 27.554497 9.586341
6 0 200 7.032527 3.355118
7 25 200 9.632828 4.039846
8 50 200 14.821584 5.659913
9 75 200 20.470692 7.791525
10 100 200 22.977827 8.901247
11 0 300 6.839360 3.355788
12 25 300 9.437649 4.070102
13 50 300 13.609004 5.545991
14 75 300 18.159601 7.387135
15 100 300 20.194335 8.380818
16 0 600 6.232509 3.330317
17 25 600 8.371084 3.990557
18 50 600 11.512385 5.235263
19 75 600 14.463214 6.605290
20 100 600 16.030137 7.467160
21 0 900 5.938640 3.338342
22 25 900 7.610695 3.891203
23 50 900 10.209530 4.917330
24 75 900 12.528651 6.157436
25 100 900 13.708622 6.791764
26 0 1200 5.841058 3.389716
27 25 1200 7.174748 3.859241
28 50 1200 9.238635 4.689011
29 75 1200 11.424713 5.688340
30 100 1200 12.349254 6.275864
t <- xtabs( temp$tht ~ temp$itpa + temp$treatment )

t <- xtabs( temp$tht ~ temp$itpa + temp$treatment )

t
temp$treatment
temp$itpa 0 100 25 50 75
100 3.362501 9.586341 4.118217 5.814391 8.264608
1200 3.389716 6.275864 3.859241 4.689011 5.688340
200 3.355118 8.901247 4.039846 5.659913 7.791525
300 3.355788 8.380818 4.070102 5.545991 7.387135
600 3.330317 7.467160 3.990557 5.235263 6.605290
900 3.338342 6.791764 3.891203 4.917330 6.157436

the factors represent real values and shouldn't be sorted as
strings. The table should read,

t
temp$treatment
temp$itpa 0 25 50 75 100
100 3.362501 4.118217 5.814391 8.264608 9.586341
200 3.355118 4.039846 5.659913 7.791525 8.901247
300 3.355788 4.070102 5.545991 7.387135 8.380818
600 3.330317 3.990557 5.235263 6.605290 7.467160
900 3.338342 3.891203 4.917330 6.157436 6.791764
1200 3.389716 3.859241 4.689011 5.688340 6.275864

this wouldn't be that big of an issue if I only did this once for the
results, but I'm using this in Sweave and need create the tables after
thousands of iterations.

Any help would be greatly appreciated.

Thanks,
Jeff.

Jeff,

Is 'itpa' supposed to be a factor?

When using your data above, read into R using read.table, treatment and
itpa are integers and the others are doubles:

str(temp)
`data.frame': 30 obs. of 4 variables:
$ treatment: int 0 25 50 75 100 0 25 50 75 100
$ itpa : int 100 100 100 100 100 200 200 200 200 200
$ qmd : num 7.29 10.46 16.67 24.03 27.55
$ tht : num 3.36 4.12 5.81 8.26 9.59

In that case, I get:

t <- xtabs(temp$tht ~ temp$itpa + temp$treatment)
t
temp$treatment
temp$itpa 0 25 50 75 100
100 3.362501 4.118217 5.814391 8.264608 9.586341
200 3.355118 4.039846 5.659913 7.791525 8.901247
300 3.355788 4.070102 5.545991 7.387135 8.380818
600 3.330317 3.990557 5.235263 6.605290 7.467160
900 3.338342 3.891203 4.917330 6.157436 6.791764
1200 3.389716 3.859241 4.689011 5.688340 6.275864

If I convert itpa to a factor with levels as you seem to have, I get:

temp$itpa <- factor(as.character(temp$itpa))
temp$itpa
[1] 100 100 100 100 100 200 200 200 200 200 300 300 300
[14] 300 300 600 600 600 600 600 900 900 900 900 900 1200
[27] 1200 1200 1200 1200
Levels: 100 1200 200 300 600 900

temp$itpa <- factor(as.character(temp$itpa))
t <- xtabs( temp$tht ~ temp$itpa + temp$treatment)
t
temp$treatment
temp$itpa 0 25 50 75 100
100 3.362501 4.118217 5.814391 8.264608 9.586341
1200 3.389716 3.859241 4.689011 5.688340 6.275864
200 3.355118 4.039846 5.659913 7.791525 8.901247
300 3.355788 4.070102 5.545991 7.387135 8.380818
600 3.330317 3.990557 5.235263 6.605290 7.467160
900 3.338342 3.891203 4.917330 6.157436 6.791764

So it would seem that you either need to change itpa back to a numeric
value in the data frame:

temp$itpa <- as.numeric(as.character(temp$itpa))
t <- xtabs(temp$tht ~ temp$itpa + temp$treatment)
t
temp$treatment
temp$itpa 0 25 50 75 100
100 3.362501 4.118217 5.814391 8.264608 9.586341
200 3.355118 4.039846 5.659913 7.791525 8.901247
300 3.355788 4.070102 5.545991 7.387135 8.380818
600 3.330317 3.990557 5.235263 6.605290 7.467160
900 3.338342 3.891203 4.917330 6.157436 6.791764
1200 3.389716 3.859241 4.689011 5.688340 6.275864

R

If you need itpa to be a factor, modify the factor levels, since they
are now ordered by the character values, not the numeric values:

temp$itpa <- factor(temp$itpa, levels = c(100, 200, 300, 600, 900,
1200))
temp$itpa
[1] 100 100 100 100 100 200 200 200 200 200 300 300 300
[14] 300 300 600 600 600 600 600 900 900 900 900 900 1200
[27] 1200 1200 1200 1200
Levels: 100 200 300 600 900 1200

t <- xtabs(temp$tht ~ temp$itpa + temp$treatment)
t
temp$treatment
temp$itpa 0 25 50 75 100
100 3.362501 4.118217 5.814391 8.264608 9.586341
200 3.355118 4.039846 5.659913 7.791525 8.901247
300 3.355788 4.070102 5.545991 7.387135 8.380818
600 3.330317 3.990557 5.235263 6.605290 7.467160
900 3.338342 3.891203 4.917330 6.157436 6.791764
1200 3.389716 3.859241 4.689011 5.688340 6.275864

HTH,

Marc Schwartz

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