Here's one way:
Vec <- rnorm(30)
Vec.cut <- cut(Vec, breaks=c(quantile(Vec, probs = seq(0, 1, by = 0.20))),
labels=c("0-20","20-40","40-60","60-80","80-100"), include.lowest=TRUE)
table(Vec.cut)
or determine the breaks automatically:
cut.size <- function(x, size) {
cut.prob <- size/length(x)
if (length(x)%%size != 0) warning("Equal sized groups only possible
by dropping some elements from x")
Vec.cut <- cut(x, breaks=c(quantile(x, probs = seq(0, 1, by =
size/length(x)))), include.lowest=TRUE)
}
CUT <- cut.size(Vec, 6)
table(CUT)
When asking for
cut.size(Vec, 7)
this will yield 4 equal-sized groups of 7, because there is no way to
perfectly split 30 observations in groups of 7 each.
HTH,
Peter
Op 18-7-2013 18:09, Marc Schwartz schreef:
Greg,
Good catch. My recollection was that the vector would be broken up into
'breaks' groups of equal size, however it is range(x) that is split into
'breaks' intervals, each of which is equal width.
Thanks,
Marc
On Jul 18, 2013, at 10:55 AM, Greg Snow <538...@gmail.com> wrote:
Marc,
Your method works fine when the data is perfectly uniform, but try it with "Vec <-
rnorm(30)" and you will see that there are more observations in the middle groups and
fewer in the tail groups. Something like quantile needs to be used to find the unequally
spaced breaks that will give equal counts within groups.
On Wed, Jul 17, 2013 at 5:04 PM, Marc Schwartz <marc_schwa...@me.com> wrote:
On Jul 17, 2013, at 4:43 PM, Witold E Wolski <wewol...@gmail.com> wrote:
I would like to "cut" a vector into groups of equal nr of elements.
looking for a function on the lines of cut but where I can specify
the size of the groups instead of the nr of groups.
In addition to the other options, if the 'breaks' argument to cut() is a single
number, rather than a vector of cut points, it defines the number of intervals
to break the 'x' vector into, which of course you can derive from length(x) /
size.
Thus:
set.seed(1)
Vec <- sample(30)
Vec
[1] 8 11 17 25 6 23 27 16 14 2 5 4 13 7 18 30 29 24 20 9 10 21
[23] 26 1 22 15 28 12 3 19
# Split into 5 groups of 6 each
split(Vec, cut(Vec, 5))
$`(0.971,6.78]`
[1] 6 2 5 4 1 3
$`(6.78,12.6]`
[1] 8 11 7 9 10 12
$`(12.6,18.4]`
[1] 17 16 14 13 18 15
$`(18.4,24.2]`
[1] 23 24 20 21 22 19
$`(24.2,30]`
[1] 25 27 30 29 26 28
Regards,
Marc Schwartz
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538...@gmail.com
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and provide commented, minimal, self-contained, reproducible code.
