I am having a hard time understanding just what 'sweep' does. The documentation states: Return an array obtained from an input array by sweeping out a summary statistic. So what does it mean "weeping out a summary statistic"? Thank you. Kevin
Either the rows or columns have a (possibly) varying argument vector
applied with an operator. The default operator is "-"/
> dtest <- matrix(1:25, nrow=5)
> dtest
[,1] [,2] [,3] [,4] [,5]
[1,] 1 6 11 16 21
[2,] 2 7 12 17 22
[3,] 3 8 13 18 23
[4,] 4 9 14 19 24
[5,] 5 10 15 20 25
> sweep(dtest, 2, 1)
[,1] [,2] [,3] [,4] [,5]
[1,] 0 5 10 15 20 # -1 argument recycling
[2,] 1 6 11 16 21
[3,] 2 7 12 17 22
[4,] 3 8 13 18 23
[5,] 4 9 14 19 24
> sweep(dtest, 2, 1:5)
[,1] [,2] [,3] [,4] [,5]
[1,] 0 4 8 12 16 # -1 -2 -3 -4 -5
[2,] 1 5 9 13 17 # |
[3,] 2 6 10 14 18 # |
[4,] 3 7 11 15 19 # \/
[5,] 4 8 12 16 20
> sweep(dtest, 1, 1:5)
[,1] [,2] [,3] [,4] [,5]
[1,] 0 5 10 15 20 # -1 --->
[2,] 0 5 10 15 20 # -2
[3,] 0 5 10 15 20 # -3
[4,] 0 5 10 15 20 # -4
[5,] 0 5 10 15 20 # -5
> sweep(dtest, 1, 1:5, FUN="+")
[,1] [,2] [,3] [,4] [,5]
[1,] 2 7 12 17 22 # +1
[2,] 4 9 14 19 24 # etc
[3,] 6 11 16 21 26
[4,] 8 13 18 23 28
[5,] 10 15 20 25 30
On Mar 16, 2009, at 10:25 PM, <rkevinburton at charter.net>
<rkevinburton at charter.net
> wrote:
> I am having a hard time understanding just what 'sweep' does. The
> documentation states:
>
> Return an array obtained from an input array by sweeping out a
> summary statistic.
>
> So what does it mean "weeping out a summary statistic"?
>
> Thank you.
>
> Kevin
>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
rkevinburton at charter.net wrote:> I am having a hard time understanding just what 'sweep' does. The documentation states: > > Return an array obtained from an input array by sweeping out a summary statistic. > > So what does it mean "weeping out a summary statistic"? >from both the text and the examples in that help page, it seems that both 'sweep' and 'summary statistics' are misleading. the argument STATS is just about any value, vector of values, array of values, etc., you might like, and these values are combined, using whatever function passed as the argument FUN, with the values in the input data. by default the combinator function FUN is '-', hence 'sweep'. in this example (from ?sweep, simplified), you're sweeping arbitrary values ('summary statistics'): A <- array(1:16, dim = c(4,4)) # sweep 1:2, with recycling sweep(A, 1, 1:2) in this example, you're multiplying ('sweeping') the data by some arbitrary values ('summary statistics'): A <- array(1:16, dim = c(4, 4)) # sweep by * 1:4, with recycling sweep(A, 1, 1:4, '*') be careful to note that here '1' means that the operation is performed *columnwise*, unlike in the case of apply, where '1' means *rowwise*: sweep(A, 1, 1:4, '*') apply(A, 1, '*', 1:4) (to make sense of the output, not that apply has implicitly transposed the matrix). be careful to note that the documentation is *wrong* wrt. the type of input and output: " Arguments: x: an array. Value: An array with the same shape as 'x', but with the summary statistics swept out. " d = data.frame(x=rnorm(10), y = rnorm(10)) is.array(d) # FALSE d = sweep(d, 1, 0) is.array(d) # FALSE no error reported, however. vQ