bug in multinominal model predictions

> set.seed(1)
> test1 <- gbm(Species ~ ., data = iris, n.trees = 1000, verbose = FALSE)
Distribution not specified, assuming multinomial ...
>
> predict(test1, head(iris), n.trees = 1000, type = "response")
        setosa versicolor  virginica
[1,] 0.8351586  0.1132224 0.05161896
[2,] 0.8327497  0.1157803 0.05147007
[3,] 0.8351586  0.1132224 0.05161896
[4,] 0.8344369  0.1139887 0.05157435
[5,] 0.8351586  0.1132224 0.05161896
[6,] 0.8348343  0.1135668 0.05159892
> predict(test1, head(iris), n.trees = c(500, 1000), type = "response")
            500       1000
 [1,] 0.6692731 0.11322242
 [2,] 0.6663942 0.11578028
 [3,] 0.6692731 0.11322242
 [4,] 0.6685032 0.11398871
 [5,] 0.6692731 0.11322242
 [6,] 0.6692731 0.11356676
 [7,] 0.8351586 0.13365581
 [8,] 0.8327497 0.13308088
 [9,] 0.8351586 0.13365581
[10,] 0.8344369 0.13350206
[11,] 0.8351586 0.13365581
[12,] 0.8348343 0.13365581
[13,] 0.1970711 0.05161896
[14,] 0.2005250 0.05147007
[15,] 0.1970711 0.05161896
[16,] 0.1979947 0.05157435
[17,] 0.1970711 0.05161896
[18,] 0.1970711 0.05159892

Looking at predict.gbm, the object predF is converted to an array of
matrices, but then:

  if (length(n.trees) > 1) {
      ## the problem is here:
      predF <- matrix(predF, ncol = length(n.trees), byrow = FALSE)
      colnames(predF) <- n.trees
      predF[, i.ntree.order] <- predF
  }

This worked with bernoulli since the results for the event were returned
(and had one dimension). It would be helpful to keep the array structure.

Thanks,

Max

> sessionInfo()
R version 2.15.2 (2012-10-26)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] splines   stats     graphics  grDevices utils     datasets  methods
[8] base

other attached packages:
[1] gbm_2.0-8        lattice_0.20-10  survival_2.36-14

loaded via a namespace (and not attached):
[1] grid_2.15.2
Original issue reported on code.google.com by harry.southworth on 5 Feb 2013 at 5:13
lishiwei2011 / gradientboostedmodels

bug in multinominal model predictions #11
