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This question covers the case where I have a list of columns, and I wish to turn them into a data.frame. What if I have a list of rows, and I wish to turn them into a data.frame?

rowList <- lapply(1:500000,function(x) sample(0:1,300,x))

The naive way to solve this is using rbind and as.data.frame, but we can't even get past the rbind step:

>Data <- do.call(rbind,vectorList)
Error: cannot allocate vector of size 572.2 Mb

What is a more efficient to do this?

Community
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Zach
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  • possible duplicate of [Most efficient list to data.frame method?](http://stackoverflow.com/questions/5942760/most-efficient-list-to-data-frame-method) – Joshua Ulrich Jan 06 '12 at 20:41
  • @JoshuaUlrich -- Are you sure it's a duplicate? Zach is asking about `rbind`ing a bunch of vectors together. The methods examined in your linked post seem to all construct data.frames by `cbind`ing or otherwise combining columns. – Josh O'Brien Jan 06 '12 at 20:59
  • @JoshO'Brien: good point. Zach needs to clarify, especially since `do.call(rbind, vectorList)` would create a matrix, not a data.frame. – Joshua Ulrich Jan 06 '12 at 21:04
  • @JoshuaUlrich: I edited my post. Please let me know if it needs further clarification. – Zach Jan 06 '12 at 21:11

2 Answers2

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It would probably be fastest / most efficient to unlist your list and fill a matrix:

> m <- matrix(unlist(vectorList), ncol=300, nrow=length(vectorList), byrow=TRUE)

But you're going to need ~6GB of RAM to do that with integer vectors and ~12GB of RAM to do it with numeric vectors.

> l <- integer(5e6*300)
> print(object.size(l),units="Gb")
5.6 Gb
Joshua Ulrich
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Try direct coercion to matrix, by relying on the column major aspect of R arrays: 

Data <- matrix(unlist(vectorList), ncol = length(vectorList[[1]]), byrow = TRUE)

If that also does not work you do not have the resources to copy this thing, so consider creating the matrix first and populating it column by column.

mdsumner
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