spread sort column names

library(data.table)
library(dplyr)
library(tidyr)
library(magrittr)

DT = data.table(stu = paste0("stu", 1:20),
  X = rnorm(20), Y = rnorm(20)) %>%
  gather(cate, values, -stu)
DT %>% spread(stu, values) %>% tbl_dt(FALSE)
#   cate        stu1      stu10     stu11      stu12       stu13     stu14
# 1    X -0.08476976  0.5428922 1.9929332 -0.6145632 -0.06098296 -1.066283
# 2    Y  0.59710869 -1.0037766 0.3508158  0.4587201 -0.13639207  1.385517
# Variables not shown: stu15 (dbl), stu16 (dbl), stu17 (dbl), stu18 (dbl),
#   stu19 (dbl), stu2 (dbl), stu20 (dbl), stu3 (dbl), stu4 (dbl), stu5 (dbl),
#   stu6 (dbl), stu7 (dbl), stu8 (dbl), stu9 (dbl)

## factorize
DT = data.table(stu = paste0("stu", 1:20),
  X = rnorm(20), Y = rnorm(20)) %>%
  gather(cate, values, -stu)
DT %>% mutate(stu = factor(stu, levels = paste0("stu", 1:20))) %>%
  spread(stu, values) %>% tbl_dt(FALSE)
#   cate      stu1      stu2      stu3      stu4       stu5       stu6
# 1    X 1.6890231 -1.300332 -1.378376 -1.874321 0.54141060 -1.2848391
# 2    Y 0.2796895  1.635385  1.048334  0.424909 0.09111916 -0.4147811
# Variables not shown: stu7 (dbl), stu8 (dbl), stu9 (dbl), stu10 (dbl), stu11
#   (dbl), stu12 (dbl), stu13 (dbl), stu14 (dbl), stu15 (dbl), stu16 (dbl),
#   stu17 (dbl), stu18 (dbl), stu19 (dbl), stu20 (dbl)

## method 1 with select
DT_spread = DT %>% spread(stu, values)
sele_names = setdiff(names(DT_spread), paste0("stu", 1:20))
col_num = match(c(sele_names, paste0("stu", 1:20)), names(DT_spread))
DT_spread %>% select(col_num) %>% tbl_dt(FALSE)
#   cate      stu1      stu2      stu3      stu4       stu5       stu6
# 1    X 1.6890231 -1.300332 -1.378376 -1.874321 0.54141060 -1.2848391
# 2    Y 0.2796895  1.635385  1.048334  0.424909 0.09111916 -0.4147811
# Variables not shown: stu7 (dbl), stu8 (dbl), stu9 (dbl), stu10 (dbl), stu11
#   (dbl), stu12 (dbl), stu13 (dbl), stu14 (dbl), stu15 (dbl), stu16 (dbl),
#   stu17 (dbl), stu18 (dbl), stu19 (dbl), stu20 (dbl)


## method 2
DT %<>% mutate(stu_num = as.integer(gsub("stu(\\d*)", "\\1", stu)),
  stu = sprintf("stu%02i", stu_num)) %>% select(-stu_num)
DT %>% spread(stu, values) %>% tbl_dt(FALSE)
#   cate     stu01     stu02     stu03     stu04      stu05      stu06
# 1    X 1.6890231 -1.300332 -1.378376 -1.874321 0.54141060 -1.2848391
# 2    Y 0.2796895  1.635385  1.048334  0.424909 0.09111916 -0.4147811
# Variables not shown: stu07 (dbl), stu08 (dbl), stu09 (dbl), stu10 (dbl),
#   stu11 (dbl), stu12 (dbl), stu13 (dbl), stu14 (dbl), stu15 (dbl), stu16
#   (dbl), stu17 (dbl), stu18 (dbl), stu19 (dbl), stu20 (dbl)