Progress bar in data.table aggregate action

Question

ddply has a .progress to get a progress bar while it\'s running, is there an equivalent for data.table in R?

Answer 1

Yes, you can use any progress status you want.

library(data.table)
dt = data.table(a=1:4, b=c("a","b"))
dt[, {cat("group:",b,"\n"); sum(a)}, b]
#group: a 
#group: b 
#   b V1
#1: a  4
#2: b  6

If you ask about progress in loading csv file with fread then it will automatically be displayed for bigger datasets. Also as mentioned by Sergey in comment you can use verbose argument to get more information, both in fread and in [.data.table.

If you want the percentage of groups processed.

grpn = uniqueN(dt$b)
dt[, {cat("progress",.GRP/grpn*100,"%\n"); sum(a)}, b]
#progress 50 % 
#progress 100 % 
#   b V1
#1: a  4
#2: b  6