r - Producing multiple qplots with data.table -

i'd produce 1 scatter plot per group data.table , return function.

i can produce different charts using plot (below) assume isn't data.table issue:

dt = data.table(a = c(1,2,3,4), b = c(1,1,2,2), c = c(4,5,6,7)) result = dt[, list(plot = list(plot(a, c))), = b] 

however if try same qplot (in order plots can return), appear end 2 copies of second chart.

dt = data.table(a = c(1,2,3,4), b = c(1,1,2,2), c = c(4,5,6,7)) result = dt[, list(plot = list(qplot(a, c))), = b] result[1,][["plot"]] result[2,][["plot"]] 

apologies if i'm missing obvious / doing stupid.

i'm not 100% sure what's going on, here workaround:

result = dt[, list(plot = list(qplot(data=.sd, a, c))), = b] 

it seems data.table reserves environment execute evaluations in in way, , qplot stores reference environment. since don't specify data argument, qplot in environment data, keeps getting changed each by value data.table, after data.table operation, last piece left there.