Making a matrix from lsmeans contrasts return - r

Question

To create the data frame:
num <- sample(1:25, 20)
x <- data.frame("Day_eclosion" = num, "Developmental" = c("AP", "MA",
"JU", "L"), "Replicate" = 1:5)
model <- glmer(Day_eclosion ~ Developmental + (1 | Replicate), family =
"poisson", data= x)
I get this return from:
a <- lsmeans(model, pairwise~Developmental, adjust = "tukey")
a$contrasts
contrast estimate SE df z.ratio p.value
AP - JU 0.2051 0.0168 Inf 12.172 <.0001
AP - L 0.3009 0.0212 Inf 14.164 <.0001
AP - MA 0.3889 0.0209 Inf 18.631 <.0001
JU - L 0.0958 0.0182 Inf 5.265 <.0001
JU - MA 0.1839 0.0177 Inf 10.387 <.0001
L - MA 0.0881 0.0222 Inf 3.964 0.0004
I am looking for a simple way to turn this output (just p values) into:
AP MA JU L
AP - <.0001 <.0001 <.0001
MA - - <.0001 0.0004
JU - - - <.0001
L - - -
I have about 20 sets of these that I need to turn into tables, so the simpler and more general the better.
Bonus points if the output is tab-deliminated, etc, so that I can easily paste into word/excel.
Thanks!

Answer 1

Here's a function that works...
pvmat = function(emm, ...) {
emm = update(emm, by = NULL) # need to work harder otherwise
pv = test(pairs(emm, reverse = TRUE, ...)) $ p.value
fmtpv = sprintf("%6.4f", pv)
fmtpv[pv < 0.0001] = "<.0001"
lbls = do.call(paste, emm#grid[emm#misc$pri.vars])
n = length(lbls)
mat = matrix("", nrow = n, ncol = n, dimnames = list(lbls, lbls))
mat[upper.tri(mat)] = fmtpv
idx = seq_len(n - 1)
mat[idx, 1 + idx] # trim off last row and 1st col
}
Illustration:
require(emmeans)
> warp.lm = lm(breaks ~ wool * tension, data = warpbreaks)
> warp.emm = emmeans(warp.lm, ~ wool * tension)
> warp.emm
wool tension emmean SE df lower.CL upper.CL
A L 44.6 3.65 48 37.2 51.9
B L 28.2 3.65 48 20.9 35.6
A M 24.0 3.65 48 16.7 31.3
B M 28.8 3.65 48 21.4 36.1
A H 24.6 3.65 48 17.2 31.9
B H 18.8 3.65 48 11.4 26.1
Confidence level used: 0.95
> pm = pvmat(warp.emm, adjust = "none")
> print(pm, quote=FALSE)
B L A M B M A H B H
A L 0.0027 0.0002 0.0036 0.0003 <.0001
B L 0.4170 0.9147 0.4805 0.0733
A M 0.3589 0.9147 0.3163
B M 0.4170 0.0584
A H 0.2682
Notes
As provided, this does not support by variables. Accordingly, the first line of the function disables them.
Using pairs(..., reverse = TRUE) generates the P values in the correct order needed later for upper.tri()
you can pass arguments to test() via ...
To create a tab-delimited version, use the clipr package:
clipr::write_clip(pm)
What you need is now in the clipboard and ready to paste into a spreadsheet.
Addendum
Answering this question inspired me to add a new function pwpm() to the emmeans package. It will appear in the next CRAN release, and is available now from the github site. It displays means and differences as well as P values; but the user may select which to include.
> pwpm(warp.emm)
wool = A
L M H
L [44.6] 0.0007 0.0009
M 20.556 [24.0] 0.9936
H 20.000 -0.556 [24.6]
wool = B
L M H
L [28.2] 0.9936 0.1704
M -0.556 [28.8] 0.1389
H 9.444 10.000 [18.8]
Row and column labels: tension
Upper triangle: P values adjust = “tukey”
Diagonal: [Estimates] (emmean)
Upper triangle: Comparisons (estimate) earlier vs. later