This should be a simple question, but I am at my wits end.
dt<-data.table(a=rep(1:10, 26), b=1:260, c=rep(1:2, 130))
sumvar <- 'mysum'
bvar <- 'b'
dt_min <- dt[, list(sumvar = sum(get(bvar))), by=list(a)]
print(dt_min)
I want the function to return two variables, "a" and
"mysum". However, it
instead returns "a" and "sumvar", rather than evaluating
"sumvar".
If I try replacing it with "get(sumvar)" or "eval(sumvar)",
R just throws
an error. What am I missing?
a sumvar
1: 1 3276
2: 2 3302
3: 3 3328
4: 4 3354
5: 5 3380
6: 6 3406
7: 7 3432
8: 8 3458
9: 9 3484
10: 10 3510
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On 27/02/2015 1:18 PM, Brian Trautman wrote:> This should be a simple question, but I am at my wits end. > > dt<-data.table(a=rep(1:10, 26), b=1:260, c=rep(1:2, 130)) > > sumvar <- 'mysum' > bvar <- 'b' > > dt_min <- dt[, list(sumvar = sum(get(bvar))), by=list(a)] > print(dt_min) > > I want the function to return two variables, "a" and "mysum". However, it > instead returns "a" and "sumvar", rather than evaluating "sumvar". > > If I try replacing it with "get(sumvar)" or "eval(sumvar)", R just throws > an error. What am I missing? > > a sumvar > 1: 1 3276 > 2: 2 3302 > 3: 3 3328 > 4: 4 3354 > 5: 5 3380 > 6: 6 3406 > 7: 7 3432 > 8: 8 3458 > 9: 9 3484 > 10: 10 3510I don't know the data.table function, but list(sumvar = sum(get(bvar))) will produce a list with one element named sumvar, holding the sum of values of a variable named 'b'. If you want that element to be named 'mysum', you could change it at the end, or construct that list as structure(list(sum(get(bvar))), names=sumvar) i.e. the full expression would be dt_min <- dt[, structure(list(sum(get(bvar))), names=sumvar), by=list(a)] The idea is that structure() produces list(sum(get(bvar))) with attribute "names" set to the contents of sumvar. Duncan Murdoch
This worked perfectly, thank you! On Fri, Feb 27, 2015 at 10:47 AM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:> On 27/02/2015 1:18 PM, Brian Trautman wrote: > > This should be a simple question, but I am at my wits end. > > > > dt<-data.table(a=rep(1:10, 26), b=1:260, c=rep(1:2, 130)) > > > > sumvar <- 'mysum' > > bvar <- 'b' > > > > dt_min <- dt[, list(sumvar = sum(get(bvar))), by=list(a)] > > print(dt_min) > > > > I want the function to return two variables, "a" and "mysum". However, > it > > instead returns "a" and "sumvar", rather than evaluating "sumvar". > > > > If I try replacing it with "get(sumvar)" or "eval(sumvar)", R just throws > > an error. What am I missing? > > > > a sumvar > > 1: 1 3276 > > 2: 2 3302 > > 3: 3 3328 > > 4: 4 3354 > > 5: 5 3380 > > 6: 6 3406 > > 7: 7 3432 > > 8: 8 3458 > > 9: 9 3484 > > 10: 10 3510 > > I don't know the data.table function, but > > list(sumvar = sum(get(bvar))) > > will produce a list with one element named sumvar, holding the sum of > values of a variable named 'b'. If you want that element to be named > 'mysum', you could change it at the end, or construct that list as > > structure(list(sum(get(bvar))), names=sumvar) > > i.e. the full expression would be > > dt_min <- dt[, structure(list(sum(get(bvar))), names=sumvar), by=list(a)] > > The idea is that structure() produces list(sum(get(bvar))) with > attribute "names" set to the contents of sumvar. > > Duncan Murdoch > >[[alternative HTML version deleted]]