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David L Carlson

2017-Jun-01 18:34 UTC

[R] Reversing one dimension of an array, in a generalized case

Here is an alternative approach using apply(). Note that with apply() you are
reversing rows or columns not indices of rows or columns so apply(junk, 2, rev)
reverses the values in each column not the column indices. We actually need to
use rev() on everything but the index we are interested in reversing:

f2 <- function(a, wh) {
    dims <- seq_len(length(dim(a)))
    dims <- setdiff(dims, wh)
    apply(apply(a, dims, rev), dims, t)
}

# Your example
j1 <- junk[ , rev(1:10), ]
j2 <- f2(junk, 2)
all.equal(j1, j2)
# [1] TRUE

# Bert's example
z1 <- f(z, 2)
z2 <- f2(z, 2)
all.equal(z1, z2)
# [1] TRUE

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352






-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Bert Gunter
Sent: Thursday, June 1, 2017 12:46 PM
To: Roy Mendelssohn - NOAA Federal <roy.mendelssohn at noaa.gov>
Cc: R-help <r-help at r-project.org>
Subject: Re: [R] Reversing one dimension of an array, in a generalized case

How about this:

f <- function(a,wh){ ## a is the array; wh is the index to be reversed
   l<- lapply(dim(a),seq_len)
   l[[wh]]<- rev(l[[wh]])
   do.call(`[`,c(list(a),l))
}

## test
z <- array(1:120,dim=2:5)

##  I omit the printouts

f(z,2)

f(z,3)


Cheers,
Bert

Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Thu, Jun 1, 2017 at 9:51 AM, Roy Mendelssohn - NOAA Federal
<roy.mendelssohn at noaa.gov> wrote:> Hi All:
>
> I have been looking for an elegant way to do the following,  but
haven't found it,  I have never had a good understanding of any of the
"apply" functions.
>
> A simplified idea is I have an array, say:
>
> junk(5, 10, 3)
>
> where  (5, 10, 3) give the dimension sizes, and I want to reverse the
second dimension, so I could do:
>
> junk1 <- junk[, rev(seq_len(10), ]
>
> but what I am after is a general function that will do that where the array
could be two, three or four dimensions,  and I pass to the function which
dimension I want to reverse, that is the function can not assume the number of
dimensions of the array nor which dimension to reverse.
>
> For example,  if i try:
>
> junk1 <- apply(junk, 2, rev)
>
> junk1 comes out as two-dimensional,  not three-dimensional.
>
> It is probably something obvious but I am not getting it.
>
> Thanks for any help.
>
> -Roy
>
>
> **********************
> "The contents of this message do not reflect any position of the U.S.
Government or NOAA."
> **********************
> Roy Mendelssohn
> Supervisory Operations Research Analyst
> NOAA/NMFS
> Environmental Research Division
> Southwest Fisheries Science Center
> ***Note new street address***
> 110 McAllister Way
> Santa Cruz, CA 95060
> Phone: (831)-420-3666
> Fax: (831) 420-3980
> e-mail: Roy.Mendelssohn at noaa.gov www: http://www.pfeg.noaa.gov/
>
> "Old age and treachery will overcome youth and skill."
> "From those who have been given much, much will be expected"
> "the arc of the moral universe is long, but it bends toward
justice" -MLK Jr.
>
> ______________________________________________
> R-help at 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.
______________________________________________
R-help at 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.

Bert Gunter

2017-Jun-01 19:00 UTC

head link

[R] Reversing one dimension of an array, in a generalized case

??
> z <- array(1:24,dim=2:4)
> all.equal(f(z,3),f2(z,3))
[1] "Attributes: < Component ?dim?: Mean relative difference: 0.4444444
>"
[2] "Mean relative difference: 0.6109091"

In fact,
> dim(f(z,3))[1] 2 3 4
> dim(f2(z,3))[1] 3 4 2

Have I made some sort of stupid error here? Or have I misunderstood
what was wanted?

Cheers,
Bert




Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Thu, Jun 1, 2017 at 11:34 AM, David L Carlson <dcarlson at tamu.edu>
wrote:> Here is an alternative approach using apply(). Note that with apply() you
are reversing rows or columns not indices of rows or columns so apply(junk, 2,
rev) reverses the values in each column not the column indices. We actually need
to use rev() on everything but the index we are interested in reversing:
>
> f2 <- function(a, wh) {
>     dims <- seq_len(length(dim(a)))
>     dims <- setdiff(dims, wh)
>     apply(apply(a, dims, rev), dims, t)
> }
>
> # Your example
> j1 <- junk[ , rev(1:10), ]
> j2 <- f2(junk, 2)
> all.equal(j1, j2)
> # [1] TRUE
>
> # Bert's example
> z1 <- f(z, 2)
> z2 <- f2(z, 2)
> all.equal(z1, z2)
> # [1] TRUE
>
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
>
>
>
>
>
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Bert
Gunter
> Sent: Thursday, June 1, 2017 12:46 PM
> To: Roy Mendelssohn - NOAA Federal <roy.mendelssohn at noaa.gov>
> Cc: R-help <r-help at r-project.org>
> Subject: Re: [R] Reversing one dimension of an array, in a generalized case
>
> How about this:
>
> f <- function(a,wh){ ## a is the array; wh is the index to be reversed
>    l<- lapply(dim(a),seq_len)
>    l[[wh]]<- rev(l[[wh]])
>    do.call(`[`,c(list(a),l))
> }
>
> ## test
> z <- array(1:120,dim=2:5)
>
> ##  I omit the printouts
>
> f(z,2)
>
> f(z,3)
>
>
> Cheers,
> Bert
>
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip
)
>
>
> On Thu, Jun 1, 2017 at 9:51 AM, Roy Mendelssohn - NOAA Federal
> <roy.mendelssohn at noaa.gov> wrote:
>> Hi All:
>>
>> I have been looking for an elegant way to do the following,  but
haven't found it,  I have never had a good understanding of any of the
"apply" functions.
>>
>> A simplified idea is I have an array, say:
>>
>> junk(5, 10, 3)
>>
>> where  (5, 10, 3) give the dimension sizes, and I want to reverse the
second dimension, so I could do:
>>
>> junk1 <- junk[, rev(seq_len(10), ]
>>
>> but what I am after is a general function that will do that where the
array could be two, three or four dimensions,  and I pass to the function which
dimension I want to reverse, that is the function can not assume the number of
dimensions of the array nor which dimension to reverse.
>>
>> For example,  if i try:
>>
>> junk1 <- apply(junk, 2, rev)
>>
>> junk1 comes out as two-dimensional,  not three-dimensional.
>>
>> It is probably something obvious but I am not getting it.
>>
>> Thanks for any help.
>>
>> -Roy
>>
>>
>> **********************
>> "The contents of this message do not reflect any position of the
U.S. Government or NOAA."
>> **********************
>> Roy Mendelssohn
>> Supervisory Operations Research Analyst
>> NOAA/NMFS
>> Environmental Research Division
>> Southwest Fisheries Science Center
>> ***Note new street address***
>> 110 McAllister Way
>> Santa Cruz, CA 95060
>> Phone: (831)-420-3666
>> Fax: (831) 420-3980
>> e-mail: Roy.Mendelssohn at noaa.gov www: http://www.pfeg.noaa.gov/
>>
>> "Old age and treachery will overcome youth and skill."
>> "From those who have been given much, much will be expected"
>> "the arc of the moral universe is long, but it bends toward
justice" -MLK Jr.
>>
>> ______________________________________________
>> R-help at 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.
>
> ______________________________________________
> R-help at 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.

David L Carlson

2017-Jun-01 19:22 UTC

head link

[R] Reversing one dimension of an array, in a generalized case

My error. Clearly I did not do enough testing.

z <- array(1:24,dim=2:4)> all.equal(f(z,1),f2(z,1))
[1] TRUE> all.equal(f(z,2),f2(z,2))
[1] TRUE> all.equal(f(z,3),f2(z,3))[1] "Attributes: < Component ?dim?: Mean relative difference: 0.4444444
>"
[2] "Mean relative difference: 0.6109091"    

# Your earlier example> z <- array(1:120, dim=2:5)
> all.equal(f(z,1),f2(z,1))
[1] TRUE> all.equal(f(z,2),f2(z,2))
[1] TRUE> all.equal(f(z,3),f2(z,3))[1] "Attributes: < Component ?dim?: Mean relative difference: 0.4444444
>"
[2] "Mean relative difference: 0.1262209"                             
> all.equal(f(z,4),f2(z,4))[1] "Attributes: < Component ?dim?: Mean relative difference: 0.5714286
>"
[2] "Mean relative difference: 0.5855162"  

David C

-----Original Message-----
From: Bert Gunter [mailto:bgunter.4567 at gmail.com] 
Sent: Thursday, June 1, 2017 2:00 PM
To: David L Carlson <dcarlson at tamu.edu>
Cc: Roy Mendelssohn - NOAA Federal <roy.mendelssohn at noaa.gov>; R-help
<r-help at r-project.org>
Subject: Re: [R] Reversing one dimension of an array, in a generalized case

??
> z <- array(1:24,dim=2:4)
> all.equal(f(z,3),f2(z,3))
[1] "Attributes: < Component ?dim?: Mean relative difference: 0.4444444
>"
[2] "Mean relative difference: 0.6109091"

In fact,
> dim(f(z,3))[1] 2 3 4
> dim(f2(z,3))[1] 3 4 2

Have I made some sort of stupid error here? Or have I misunderstood
what was wanted?

Cheers,
Bert




Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Thu, Jun 1, 2017 at 11:34 AM, David L Carlson <dcarlson at tamu.edu>
wrote:> Here is an alternative approach using apply(). Note that with apply() you
are reversing rows or columns not indices of rows or columns so apply(junk, 2,
rev) reverses the values in each column not the column indices. We actually need
to use rev() on everything but the index we are interested in reversing:
>
> f2 <- function(a, wh) {
>     dims <- seq_len(length(dim(a)))
>     dims <- setdiff(dims, wh)
>     apply(apply(a, dims, rev), dims, t)
> }
>
> # Your example
> j1 <- junk[ , rev(1:10), ]
> j2 <- f2(junk, 2)
> all.equal(j1, j2)
> # [1] TRUE
>
> # Bert's example
> z1 <- f(z, 2)
> z2 <- f2(z, 2)
> all.equal(z1, z2)
> # [1] TRUE
>
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
>
>
>
>
>
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Bert
Gunter
> Sent: Thursday, June 1, 2017 12:46 PM
> To: Roy Mendelssohn - NOAA Federal <roy.mendelssohn at noaa.gov>
> Cc: R-help <r-help at r-project.org>
> Subject: Re: [R] Reversing one dimension of an array, in a generalized case
>
> How about this:
>
> f <- function(a,wh){ ## a is the array; wh is the index to be reversed
>    l<- lapply(dim(a),seq_len)
>    l[[wh]]<- rev(l[[wh]])
>    do.call(`[`,c(list(a),l))
> }
>
> ## test
> z <- array(1:120,dim=2:5)
>
> ##  I omit the printouts
>
> f(z,2)
>
> f(z,3)
>
>
> Cheers,
> Bert
>
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip
)
>
>
> On Thu, Jun 1, 2017 at 9:51 AM, Roy Mendelssohn - NOAA Federal
> <roy.mendelssohn at noaa.gov> wrote:
>> Hi All:
>>
>> I have been looking for an elegant way to do the following,  but
haven't found it,  I have never had a good understanding of any of the
"apply" functions.
>>
>> A simplified idea is I have an array, say:
>>
>> junk(5, 10, 3)
>>
>> where  (5, 10, 3) give the dimension sizes, and I want to reverse the
second dimension, so I could do:
>>
>> junk1 <- junk[, rev(seq_len(10), ]
>>
>> but what I am after is a general function that will do that where the
array could be two, three or four dimensions,  and I pass to the function which
dimension I want to reverse, that is the function can not assume the number of
dimensions of the array nor which dimension to reverse.
>>
>> For example,  if i try:
>>
>> junk1 <- apply(junk, 2, rev)
>>
>> junk1 comes out as two-dimensional,  not three-dimensional.
>>
>> It is probably something obvious but I am not getting it.
>>
>> Thanks for any help.
>>
>> -Roy
>>
>>
>> **********************
>> "The contents of this message do not reflect any position of the
U.S. Government or NOAA."
>> **********************
>> Roy Mendelssohn
>> Supervisory Operations Research Analyst
>> NOAA/NMFS
>> Environmental Research Division
>> Southwest Fisheries Science Center
>> ***Note new street address***
>> 110 McAllister Way
>> Santa Cruz, CA 95060
>> Phone: (831)-420-3666
>> Fax: (831) 420-3980
>> e-mail: Roy.Mendelssohn at noaa.gov www: http://www.pfeg.noaa.gov/
>>
>> "Old age and treachery will overcome youth and skill."
>> "From those who have been given much, much will be expected"
>> "the arc of the moral universe is long, but it bends toward
justice" -MLK Jr.
>>
>> ______________________________________________
>> R-help at 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.
>
> ______________________________________________
> R-help at 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.

Ismail SEZEN

2017-Jun-01 19:40 UTC

head link

[R] Reversing one dimension of an array, in a generalized case

And my 2 cents,

Rev <- function(x, margin) {
    newdim <- rep("", length(dim(x)))
    newdim[margin] <- paste(dim(x), ":1", sep =
"")[margin]
    z <- eval(parse(text = gettextf("x[%s,drop = F]", paste(newdim,
sep = "",
                                                            collapse =
","))))
    class(z) <- oldClass(x)
    return(z)
}

z <- array(1:24,dim=2:4)
dim(f(z, 3)) # 2 3 4
dim(f2(z, 3)) # 3 4 2
dim(Rev(z, 3)) # 2 3 4
dim(revdim(z,3)) # 2 3 4

microbenchmark::microbenchmark(f(z, 3), Rev(z, 3), revdim(z,3), f2(z,3))

Unit: microseconds
         expr     min       lq      mean   median       uq     max neval
      f(z, 3)   6.356   7.6090   9.74268   9.3285  11.2325  35.571   100
    Rev(z, 3) 161.079 166.9660 175.26906 172.1450 176.8130 273.078   100
 revdim(z, 3)   5.011   6.1300   7.88565   7.5695   9.0500  21.301   100
     f2(z, 3)  68.454  71.6815  82.85703  81.6700  87.9285 126.496   100

and strangely,

all.equal(f(z, 3), Rev(z, 3), revdim(z,3), f2(z,3))
[1] TRUE

?
> On 1 Jun 2017, at 22:00, Bert Gunter <bgunter.4567 at gmail.com>
wrote:
> 
> ??
> 
>> z <- array(1:24,dim=2:4)
>> all.equal(f(z,3),f2(z,3))
> 
> [1] "Attributes: < Component ?dim?: Mean relative difference:
0.4444444 >"
> [2] "Mean relative difference: 0.6109091"
> 
> In fact,
> 
>> dim(f(z,3))
> [1] 2 3 4
> 
>> dim(f2(z,3))
> [1] 3 4 2
> 
> Have I made some sort of stupid error here? Or have I misunderstood
> what was wanted?
> 
> Cheers,
> Bert
> 
> 
> 
> 
> Bert Gunter
> 
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip
)
> 
> 
> On Thu, Jun 1, 2017 at 11:34 AM, David L Carlson <dcarlson at
tamu.edu> wrote:
>> Here is an alternative approach using apply(). Note that with apply()
you are reversing rows or columns not indices of rows or columns so apply(junk,
2, rev) reverses the values in each column not the column indices. We actually
need to use rev() on everything but the index we are interested in reversing:
>> 
>> f2 <- function(a, wh) {
>>    dims <- seq_len(length(dim(a)))
>>    dims <- setdiff(dims, wh)
>>    apply(apply(a, dims, rev), dims, t)
>> }
>> 
>> # Your example
>> j1 <- junk[ , rev(1:10), ]
>> j2 <- f2(junk, 2)
>> all.equal(j1, j2)
>> # [1] TRUE
>> 
>> # Bert's example
>> z1 <- f(z, 2)
>> z2 <- f2(z, 2)
>> all.equal(z1, z2)
>> # [1] TRUE
>> 
>> -------------------------------------
>> David L Carlson
>> Department of Anthropology
>> Texas A&M University
>> College Station, TX 77840-4352
>> 
>> 
>> 
>> 
>> 
>> 
>> -----Original Message-----
>> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Bert
Gunter
>> Sent: Thursday, June 1, 2017 12:46 PM
>> To: Roy Mendelssohn - NOAA Federal <roy.mendelssohn at noaa.gov>
>> Cc: R-help <r-help at r-project.org>
>> Subject: Re: [R] Reversing one dimension of an array, in a generalized
case
>> 
>> How about this:
>> 
>> f <- function(a,wh){ ## a is the array; wh is the index to be
reversed
>>   l<- lapply(dim(a),seq_len)
>>   l[[wh]]<- rev(l[[wh]])
>>   do.call(`[`,c(list(a),l))
>> }
>> 
>> ## test
>> z <- array(1:120,dim=2:5)
>> 
>> ##  I omit the printouts
>> 
>> f(z,2)
>> 
>> f(z,3)
>> 
>> 
>> Cheers,
>> Bert
>> 
>> Bert Gunter
>> 
>> "The trouble with having an open mind is that people keep coming
along
>> and sticking things into it."
>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic
strip )
>> 
>> 
>> On Thu, Jun 1, 2017 at 9:51 AM, Roy Mendelssohn - NOAA Federal
>> <roy.mendelssohn at noaa.gov> wrote:
>>> Hi All:
>>> 
>>> I have been looking for an elegant way to do the following,  but
haven't found it,  I have never had a good understanding of any of the
"apply" functions.
>>> 
>>> A simplified idea is I have an array, say:
>>> 
>>> junk(5, 10, 3)
>>> 
>>> where  (5, 10, 3) give the dimension sizes, and I want to reverse
the second dimension, so I could do:
>>> 
>>> junk1 <- junk[, rev(seq_len(10), ]
>>> 
>>> but what I am after is a general function that will do that where
the array could be two, three or four dimensions,  and I pass to the function
which dimension I want to reverse, that is the function can not assume the
number of dimensions of the array nor which dimension to reverse.
>>> 
>>> For example,  if i try:
>>> 
>>> junk1 <- apply(junk, 2, rev)
>>> 
>>> junk1 comes out as two-dimensional,  not three-dimensional.
>>> 
>>> It is probably something obvious but I am not getting it.
>>> 
>>> Thanks for any help.
>>> 
>>> -Roy
>>> 
>>> 
>>> **********************
>>> "The contents of this message do not reflect any position of
the U.S. Government or NOAA."
>>> **********************
>>> Roy Mendelssohn
>>> Supervisory Operations Research Analyst
>>> NOAA/NMFS
>>> Environmental Research Division
>>> Southwest Fisheries Science Center
>>> ***Note new street address***
>>> 110 McAllister Way
>>> Santa Cruz, CA 95060
>>> Phone: (831)-420-3666
>>> Fax: (831) 420-3980
>>> e-mail: Roy.Mendelssohn at noaa.gov www: http://www.pfeg.noaa.gov/
>>> 
>>> "Old age and treachery will overcome youth and skill."
>>> "From those who have been given much, much will be
expected"
>>> "the arc of the moral universe is long, but it bends toward
justice" -MLK Jr.
>>> 
>>> ______________________________________________
>>> R-help at 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.
>> 
>> ______________________________________________
>> R-help at 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.
> 
> ______________________________________________
> R-help at 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.

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