On the off chance that anyone is still interested, here is the corrected
function using aperm():
z <- array(1:120,dim=2:5)
f2 <- function(a, wh) {
idx <- seq_len(length(dim(a)))
dims <- setdiff(idx, wh)
idx <- append(idx[-1], idx[1], wh-1)
aperm(apply(a, dims, rev), idx)
}
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] TRUE
all.equal(f(z, 4), f2(z, 4))
# [1] TRUE
David C
From: Ismail SEZEN [mailto:[email protected]]
Sent: Thursday, June 1, 2017 3:35 PM
To: Roy Mendelssohn - NOAA Federal <[email protected]>
Cc: David L Carlson <[email protected]>; R-help <[email protected]>
Subject: Re: [R] Reversing one dimension of an array, in a generalized case
On 1 Jun 2017, at 22:42, Roy Mendelssohn - NOAA Federal
<[email protected]> wrote:
Thanks to all for responses/. There was a question of exactly what was wanted.
It is the generalization of the obvious example I gave,
junk1 <- junk[, rev(seq_len(10), ]
so that
junk[1,1,1 ] = junk1[1,10,1]
junk[1,2,1] = junk1[1,9,1]
etc.
The genesis of this is the program is downloading data from a variety of
sources on (time, altitude, lat, lon) coordinates, but all the coordinates are
not always there, and sometime the latitude coordinates go from north to south
and sometimes from south to north. I want to always return the data going from
south to north, so if I find that the data is north to south, I have to first
reverse the array with the coordinate values (easy enough), and then reverse
the one dimension in the data array that corresponds to latitude. The
downloaded information tells me which dimension is latitude plus how many
coordinates are in the data.
Hello Roy,
Perhaps you are aware of but I want to mention anyway. Basic issue is that you
always want latitudes are monotonously increasing. Let me tell what I do when I
read a ncdf file:
1- Set latitudes always monotonously decreasing (from 90 to -90)
2- Set longitudes always mononously increasing but from -180 to 180.
3- Set levels always monotonously decreasing (this is not relevant)
Why? If you plan to plot variables in R, you will need coordinates in this
order. For instance, if you set latitudes monotonously increasing, your map
will be plotted upside down. To fix this, you will need reverse dimension
again. And also if your longitudes ranges from 0 to 360, you will see the only
the east side of the plot on a world map. West of Greencwich will be empty.
They were the problems that I faced last year when I tried to plot netcdf files
using lattice and rasterVis packages.
As I the said, I haven't done extensive testing on what Bert sent, but on a
toy 3-dimensional example I have it appeared to do what I want.
Thanks again,
-Roy
On Jun 1, 2017, at 12:22 PM, David L Carlson <[email protected]> wrote:
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:[email protected]]
Sent: Thursday, June 1, 2017 2:00 PM
To: David L Carlson <[email protected]>
Cc: Roy Mendelssohn - NOAA Federal <[email protected]>; R-help
<[email protected]>
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 <[email protected]> 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:[email protected]] On Behalf Of Bert Gunter
Sent: Thursday, June 1, 2017 12:46 PM
To: Roy Mendelssohn - NOAA Federal <[email protected]>
Cc: R-help <[email protected]>
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
<[email protected]> 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: [email protected] 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.
______________________________________________
[email protected] 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.
______________________________________________
[email protected] 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 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: [email protected] 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.
______________________________________________
[email protected] 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.
______________________________________________
[email protected] 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.
