Sequence expansion question
I have a sequence of 'endpoints', e.g.:
c(7,10,5,11,15)
that I want to expand to a sequence of 'elapsed time' between the endpoints, e.g.
c(7,1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,1,2,3,4,5,6,7,8,9,10,11,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15)
Whats the most efficient way to do this in R? I'm imagining some creative use of the embed
function, but I can't quite get there without using a ugly for
loop.
Here's the naive开发者_StackOverflow中文版 way to do this:
expandSequence <- function(x) {
out <- x[1]
for (y in (x[-1])) {
out <- c(out,seq(1,y))
}
return(out)
}
expandSequence(c(7,10,5,11,15))
There is a base function to do this, called, wait for it, sequence
:
sequence(c(7,10,5,11,15))
[1] 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 1 2 3
[26] 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
In your case it seems your first endpoint is in fact not part of the sequence, so it becomes:
c(7, sequence(c(10,5,11,15)))
[1] 7 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 1 2 3 4 5 6 7 8 9
[26] 10 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
How about this:
> unlist(sapply(x,seq))
[1] 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 1 2
[25] 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
With the first element added on at the end:
c( x[1], unlist( sapply( x[seq(2,length(x))], seq ) ) )
And a slightly more readable version:
library(taRifx)
c( x[1], unlist( sapply( shift(x,wrap=FALSE), seq ) ) )
A combination of lapply()
and seq_len()
is useful here:
expandSequence <- function(x) {
out <- lapply(x[-1], seq_len)
do.call(c, c(x[1], out))
}
Which gives for
pts <- c(7,10,5,11,15)
> expandSequence(pts)
[1] 7 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 1 2 3 4
[21] 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11 12 13
[41] 14 15
(An alternative is:
expandSequence <- function(x) {
out <- lapply(x[-1], seq_len)
unlist(c(x[1], out), use.names = FALSE)
}
)
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