Is there a way to extract continuous feature in an 2D array
Say I have an array of number
a <- c(1,2,3,6,7,8,9,10,20)
if the开发者_StackOverflowre a way to tell R to output just the range of the continuous sequence from "a" e.g., the continuous sequences in "a" are the following
1,3 6,10 20
Thanks a lot! Derek
I don't think there is a straight way, but you could create two logical vectors telling you if next/previous element is 1 greatest/least. E.g.:
data.frame(
a,
is_first = c(TRUE,diff(a)!=1),
is_last = c(diff(a)!=1,TRUE)
)
# Gives you:
a is_first is_last
1 1 TRUE FALSE
2 2 FALSE FALSE
3 3 FALSE TRUE
4 6 TRUE FALSE
5 7 FALSE FALSE
6 8 FALSE FALSE
7 9 FALSE FALSE
8 10 FALSE TRUE
9 20 TRUE TRUE
So ranges are:
cbind(a[c(TRUE,diff(a)!=1)], a[c(diff(a)!=1,TRUE)])
[1,] 1 3
[2,] 6 10
[3,] 20 20
I did this (not so elegant I admit) in case you want all the numbers of each sequence in a list
a <- c(1,2,3,6,7,8,9,10,20)
z <- c(1,which(c(1,diff(a))!=1))
g <- lapply(seq(1:length(z)),function(i) {
if (i < length(z)) a[z[i] : (z[i+1] - 1)]
else a[z[i] : length(a)]
})
[[1]]
[1] 1 2 3
[[2]]
[1] 6 7 8 9 10
[[3]]
[1] 20
Then you can get a 2D array with something like this
sapply(g,function(x) c(x[1],x[length(x)]))
[,1] [,2] [,3]
[1,] 1 6 20
[2,] 3 10 20
> a <- c(1,2,3,6,7,8,9,10,20)
> N<-length(a)
> k<-2:(N-1)
> z<-(a[k-1]+1)!=a[k] | (a[k+1]-1)!=a[k]
> c(a[1],a[k][z],a[N])
[1] 1 3 6 10 20
精彩评论