Unsplitting a data frame by a variable (different length of factors)

Question

I have a data frame (st1) that I split by a factor. I then performed functions to the split data (i.e. mean) by another factor and hence, I cannot perform unsplit any more because my original data frame is of different length now.

As to walk you through what I did, here is a code:

NT = data.table(st1)

NT2=split (NT, NT$bin)

NT3 <- data.frame(sapply( NT2 , function(x) x[, list(ang=length(unique(thetadeg)), len=length(T), Vm=mean(V)), by=c("A")]))

head of the st1:

structure(list(A = c(25L, 25L, 25L, 25L, 25L, 25L), T = 56:61, X = c(481.07, 487.04, 490.03, 499, 504.97, 507.96), Y = c(256.97, 256.97, 256.97, 256.97, 256.97, 256.97), V = c(4.482, 5.976, 7.47, 4.482, 5.976, 7.47), thetarad = c(0.164031585831919, 0.169139558949956, 0.171661200692621, 0.179083242584008, 0.183907246800473, 0.186289411097781), thetadeg = c(9.39831757286096, 9.69098287432395, 9.83546230358968, 10.2607139792383, 10.537109061132, 10.6735970214433), bin = structure(c(1L, 1L, 1L, 1L, 1L, 1L), .Label = c("binA", "binB", "binC", "outbin"), class = "factor")), .Names = c("A", "T", "X", "Y", "V", "thetarad", "thetadeg", "bin"), row.names = c(NA, 6L), class = "data.frame")

I did not put a dput(head) for my NT3 because it will be too long.

I tried unsplit, unlist but am not successful. What I want to do is to have one data frame again with the bin as a factor.

Any help would be great.

edit: What I would like my data frame to have is A, ang, len, Vm, and bin as headers.

It might make more sense to, instead of using split, simply use the by=bin argument in data.table — Ricardo Saporta
Take a look at the Intro to data.table. You probably need from page 6 onwards, fast grouping section. — marbel

Ricardo Saporta Ricardo Saporta · Accepted Answer · 2014-01-30T22:18:34

It's not altogether clear what your intended output is, but looking at what you have for NT3, this may be more effective:

NT <- data.table(ST1, key="A")
NT[, list(ang=length(unique(thetadeg))
              , len=length(T)
              , Vm=mean(V))
   , by=list(A, bin) ]

Unsplitting a data frame by a variable (different length of factors)

2 Answers