test

library(data.table)
library(dplyr)
library(magrittr)
N = 20000
T = 10
nItem = 500
m = matrix(rbinom(N*T*nItem, 15, 0.4), N)
dat = data.table(id = 1:nrow(m), m) %>%
  setnames(paste0("V",1:(T*nItem)), paste0(
  rep(paste0('item', 1:nItem),,, T), '_', rep(1:T, nItem)))

## method 1
st = proc.time()
varChecking = names(dat)[grepl("item\\d+_1$", names(dat))]
f = function(x) ifelse(x < 5, 0, x)
dat_out = mutate_each_(dat, funs(f), varChecking)
namesWorking = gsub("(item\\d+_)1", "\\1", varChecking)
varsWorking = paste0(rep(namesWorking,,,T-1), rep(2:T,nItem))
cmd = paste0('ifelse(', rep(namesWorking,,,T-1), '1<5,0,',
    varsWorking, ')')
dat_out %<>% mutate_(.dots= setNames(lapply(cmd, lazyeval:::interp), varsWorking))
proc.time() - st
#   user  system elapsed
#  65.48    0.23   68.03

## method 2
st = proc.time()
varChecking = names(dat)[grepl("item\\d+_1$", names(dat))]
f = function(x) ifelse(x < 5, 0, x)
dat_out = mutate_each_(dat, funs(f), varChecking)
namesWorking = gsub("(item\\d+_)1", "\\1", varChecking)
varsWorking = paste0(rep(namesWorking,,,T-1), rep(2:T,nItem))
eval(parse(text = paste0('dat_out=mutate(dat_out,',
  paste0(varsWorking, '=ifelse(', rep(namesWorking,,,T-1), '1<5,0,',
    varsWorking, ')', collapse = ","), ')')))
proc.time() - st
#   user  system elapsed
#  64.12    0.26   66.75

st = proc.time()
varWorking = gsub('(item\\d+_)\\d+$', '\\1', names(dat)) %>%
  unique %>% setdiff('id')
dat_out = llply(varWorking, function(x){
  tmp_dat = dat %>% select(starts_with(x))
  tmp_dat %<>% setnames(paste0("V", 1:ncol(tmp_dat)))
  f = function(x) ifelse(tmp_dat$V1 > 5, x, 0)
  tmp_dat %<>% mutate_each(funs(f)) %>%
    setnames(paste0(x, 1:ncol(tmp_dat)))
  tmp_dat
}) %>% bind_cols %>% tbl_dt %>% mutate(id = dat$id)
proc.time() - st
#   user  system elapsed
#  51.41    0.50   53.87