[R] counting sets of consecutive integers in a vector
I have a vector of sorted positive integer values (e.g., postive integers after applying sort() and unique()). For example, this: c(1,2,5,6,7,8,25,30,31,32,33) I want to make a matrix from that vector that has two columns: (1) the first value in every run of consecutive integer values, and (2) the corresponding number of consecutive values. For example: c(1:20) would become this... 1 20 ...because there are 20 consecutive integers beginning with 1 and c(1,2,5,6,7,8,25,30,31,32,33) would become 1 2 5 4 25 1 30 4 What would be the best way to accomplish this? Here is my first effort: v - c(1,2,5,6,7,8,25,30,31,32,33) L - rle( v - 1:length(v) )$lengths n - length( L ) matrix( c( v[ c( 1, cumsum(L)+1 ) ][1:n], L), nrow=n) [,1] [,2] [1,]12 [2,]54 [3,] 251 [4,] 304 I suppose that works well enough, but there may be a better way, and besides, I wouldn't want to deny anyone here the opportunity to solve a fun puzzle. ;-) The use for this is that I will be doing repeated seeks of a binary file to extract data. seek() gives the starting point and readBin(n=X) gives the number of bytes to read. So when there are many consecutive variables to be read, I can multiply the X in n=X by that number instead of doing many different seek() calls. (The data are in a transposed format where I read in every record for some variable as sequential elements.) I'm probably not the first person to deal with this. Best, Mike -- Michael B. Miller, Ph.D. University of Minnesota http://scholar.google.com/citations?user=EV_phq4J __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] counting sets of consecutive integers in a vector
Tena koe Mike
An alternative, which is slightly fast:
diffv - diff(v)
starts - c(1, which(diffv!=1)+1)
cbind(v[starts], c(diff(starts), length(v)-starts[length(starts)]+1))
Peter Alspach
-Original Message-
From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Mike Miller
Sent: Monday, 5 January 2015 1:03 p.m.
To: R-Help List
Subject: [R] counting sets of consecutive integers in a vector
I have a vector of sorted positive integer values (e.g., postive integers after
applying sort() and unique()). For example, this:
c(1,2,5,6,7,8,25,30,31,32,33)
I want to make a matrix from that vector that has two columns: (1) the first
value in every run of consecutive integer values, and (2) the corresponding
number of consecutive values. For example:
c(1:20) would become this...
1 20
...because there are 20 consecutive integers beginning with 1 and
c(1,2,5,6,7,8,25,30,31,32,33) would become
1 2
5 4
25 1
30 4
What would be the best way to accomplish this? Here is my first effort:
v - c(1,2,5,6,7,8,25,30,31,32,33)
L - rle( v - 1:length(v) )$lengths
n - length( L )
matrix( c( v[ c( 1, cumsum(L)+1 ) ][1:n], L), nrow=n)
[,1] [,2]
[1,]12
[2,]54
[3,] 251
[4,] 304
I suppose that works well enough, but there may be a better way, and besides, I
wouldn't want to deny anyone here the opportunity to solve a fun puzzle. ;-)
The use for this is that I will be doing repeated seeks of a binary file to
extract data. seek() gives the starting point and readBin(n=X) gives the
number of bytes to read. So when there are many consecutive variables to be
read, I can multiply the X in n=X by that number instead of doing many
different seek() calls. (The data are in a transposed format where I read in
every record for some variable as sequential elements.) I'm probably not the
first person to deal with this.
Best,
Mike
--
Michael B. Miller, Ph.D.
University of Minnesota
http://scholar.google.com/citations?user=EV_phq4J
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Re: [R] counting sets of consecutive integers in a vector
Here is another approach:
v - c(1,2,5,6,7,8,25,30,31,32,33)
# split by differences != 1
t(sapply(split(v, cumsum(c(1, diff(v)) != 1)), function(x){
+ c(value = x[1L], length = length(x)) # output first value and length
+ }))
value length
0 1 2
1 5 4
225 1
330 4
Jim Holtman
Data Munger Guru
What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.
On Sun, Jan 4, 2015 at 8:27 PM, Peter Alspach
peter.alsp...@plantandfood.co.nz wrote:
Tena koe Mike
An alternative, which is slightly fast:
diffv - diff(v)
starts - c(1, which(diffv!=1)+1)
cbind(v[starts], c(diff(starts), length(v)-starts[length(starts)]+1))
Peter Alspach
-Original Message-
From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Mike
Miller
Sent: Monday, 5 January 2015 1:03 p.m.
To: R-Help List
Subject: [R] counting sets of consecutive integers in a vector
I have a vector of sorted positive integer values (e.g., postive integers
after applying sort() and unique()). For example, this:
c(1,2,5,6,7,8,25,30,31,32,33)
I want to make a matrix from that vector that has two columns: (1) the
first value in every run of consecutive integer values, and (2) the
corresponding number of consecutive values. For example:
c(1:20) would become this...
1 20
...because there are 20 consecutive integers beginning with 1 and
c(1,2,5,6,7,8,25,30,31,32,33) would become
1 2
5 4
25 1
30 4
What would be the best way to accomplish this? Here is my first effort:
v - c(1,2,5,6,7,8,25,30,31,32,33)
L - rle( v - 1:length(v) )$lengths
n - length( L )
matrix( c( v[ c( 1, cumsum(L)+1 ) ][1:n], L), nrow=n)
[,1] [,2]
[1,]12
[2,]54
[3,] 251
[4,] 304
I suppose that works well enough, but there may be a better way, and
besides, I wouldn't want to deny anyone here the opportunity to solve a fun
puzzle. ;-)
The use for this is that I will be doing repeated seeks of a binary file
to extract data. seek() gives the starting point and readBin(n=X) gives
the number of bytes to read. So when there are many consecutive variables
to be read, I can multiply the X in n=X by that number instead of doing
many different seek() calls. (The data are in a transposed format where I
read in every record for some variable as sequential elements.) I'm
probably not the first person to deal with this.
Best,
Mike
--
Michael B. Miller, Ph.D.
University of Minnesota
http://scholar.google.com/citations?user=EV_phq4J
__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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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.
The contents of this e-mail are confidential and may be ...{{dropped:14}}
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[[alternative HTML version deleted]]
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Re: [R] counting sets of consecutive integers in a vector
Here is a solution using data.table require(data.table) x - data.table(v, diff = cumsum(c(1, diff(v)) != 1)) x v diff 1: 10 2: 20 3: 51 4: 61 5: 71 6: 81 7: 252 8: 303 9: 313 10: 323 11: 333 x[, list(value = v[1L], length = .N), key = 'diff'] diff value length 1:0 1 2 2:1 5 4 3:225 1 4:330 4 x[, list(value = v[1L], length = .N), key = 'diff'][, -1, with = FALSE] # get rid of 'diff' column value length 1: 1 2 2: 5 4 3:25 1 4:30 4 Jim Holtman Data Munger Guru What is the problem that you are trying to solve? Tell me what you want to do, not how you want to do it. On Sun, Jan 4, 2015 at 7:03 PM, Mike Miller mbmille...@gmail.com wrote: I have a vector of sorted positive integer values (e.g., postive integers after applying sort() and unique()). For example, this: c(1,2,5,6,7,8,25,30,31,32,33) I want to make a matrix from that vector that has two columns: (1) the first value in every run of consecutive integer values, and (2) the corresponding number of consecutive values. For example: c(1:20) would become this... 1 20 ...because there are 20 consecutive integers beginning with 1 and c(1,2,5,6,7,8,25,30,31,32,33) would become 1 2 5 4 25 1 30 4 What would be the best way to accomplish this? Here is my first effort: v - c(1,2,5,6,7,8,25,30,31,32,33) L - rle( v - 1:length(v) )$lengths n - length( L ) matrix( c( v[ c( 1, cumsum(L)+1 ) ][1:n], L), nrow=n) [,1] [,2] [1,]12 [2,]54 [3,] 251 [4,] 304 I suppose that works well enough, but there may be a better way, and besides, I wouldn't want to deny anyone here the opportunity to solve a fun puzzle. ;-) The use for this is that I will be doing repeated seeks of a binary file to extract data. seek() gives the starting point and readBin(n=X) gives the number of bytes to read. So when there are many consecutive variables to be read, I can multiply the X in n=X by that number instead of doing many different seek() calls. (The data are in a transposed format where I read in every record for some variable as sequential elements.) I'm probably not the first person to deal with this. Best, Mike -- Michael B. Miller, Ph.D. University of Minnesota http://scholar.google.com/citations?user=EV_phq4J __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/ posting-guide.html and provide commented, minimal, self-contained, reproducible code. [[alternative HTML version deleted]] __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] counting sets of consecutive integers in a vector
Thanks, Peter. Why not cbind your idea for the first column with my idea for the second column and get it done in one line?: v - c(1,2,5,6,7,8,25,30,31,32,33) M - cbind( v[ c(1, which( diff(v) !=1 ) + 1 ) ] , rle( v - 1:length(v) )$lengths ) M [,1] [,2] [1,]12 [2,]54 [3,] 251 [4,] 304 I find that pretty appealing and I'll probably stick with it. It seems quite fast. Here's an example: # make fairly long vector v - sort(unique(round(10*runif(10 length(v) [1] 63274 # time the procedure: ptm - proc.time() ; M - cbind( v[ c(1, which( diff(v) !=1 ) + 1 ) ] , rle( v - 1:length(v) )$lengths ) ; proc.time() - ptm user system elapsed 0.030.000.03 dim(M) [1] 23212 2 I probably won't be using vectors any longer than that, and this isn't the kind of thing that I do over and over again, so that speed is excellent. Mike On Mon, 5 Jan 2015, Peter Alspach wrote: Tena koe Mike An alternative, which is slightly fast: diffv - diff(v) starts - c(1, which(diffv!=1)+1) cbind(v[starts], c(diff(starts), length(v)-starts[length(starts)]+1)) Peter Alspach -Original Message- From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Mike Miller Sent: Monday, 5 January 2015 1:03 p.m. To: R-Help List Subject: [R] counting sets of consecutive integers in a vector I have a vector of sorted positive integer values (e.g., postive integers after applying sort() and unique()). For example, this: c(1,2,5,6,7,8,25,30,31,32,33) I want to make a matrix from that vector that has two columns: (1) the first value in every run of consecutive integer values, and (2) the corresponding number of consecutive values. For example: c(1:20) would become this... 1 20 ...because there are 20 consecutive integers beginning with 1 and c(1,2,5,6,7,8,25,30,31,32,33) would become 1 2 5 4 25 1 30 4 What would be the best way to accomplish this? Here is my first effort: v - c(1,2,5,6,7,8,25,30,31,32,33) L - rle( v - 1:length(v) )$lengths n - length( L ) matrix( c( v[ c( 1, cumsum(L)+1 ) ][1:n], L), nrow=n) [,1] [,2] [1,]12 [2,]54 [3,] 251 [4,] 304 I suppose that works well enough, but there may be a better way, and besides, I wouldn't want to deny anyone here the opportunity to solve a fun puzzle. ;-) The use for this is that I will be doing repeated seeks of a binary file to extract data. seek() gives the starting point and readBin(n=X) gives the number of bytes to read. So when there are many consecutive variables to be read, I can multiply the X in n=X by that number instead of doing many different seek() calls. (The data are in a transposed format where I read in every record for some variable as sequential elements.) I'm probably not the first person to deal with this. Best, Mike -- Michael B. Miller, Ph.D. University of Minnesota http://scholar.google.com/citations?user=EV_phq4J __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. The contents of this e-mail are confidential and may be subject to legal privilege. If you are not the intended recipient you must not use, disseminate, distribute or reproduce all or any part of this e-mail or attachments. If you have received this e-mail in error, please notify the sender and delete all material pertaining to this e-mail. Any opinion or views expressed in this e-mail are those of the individual sender and may not represent those of The New Zealand Institute for Plant and Food Research Limited. __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
