Re: [Rd] Unexpected behavior of '[' in an apply instruction

2021-02-12 Thread Avi Gross via R-devel 
Just to be different, the premise was that you do not know how many dimensions 
the array had. But that is easily available using dim() including how many 
items are in each dimension. So, in principle, you can use a normal indexing 
method perhaps in a loop to get what you want. Not sexy but doable. You can 
treat the array x as a vector just like lower level R does and access the 
contents using the formula it uses.

-Original Message-
From: R-devel  On Behalf Of Sokol Serguei
Sent: Friday, February 12, 2021 5:50 PM
To: r-devel@r-project.org
Subject: Re: [Rd] Unexpected behavior of '[' in an apply instruction

Le 12/02/2021 à 22:23, Rui Barradas a écrit :
> Hello,
>
> Yes, although there is an accepted solution, I believe you should post 
> this solution there. It's a base R solution, what the question asks for.
>
> And thanks, I would have never reminded myself of slice.index.

There is another approach -- produce a call to `[`() putting there "required 
number of commas in their proper places" programmatically. 
Even if it does not lead to a very readable expression, I think it merits to be 
mentioned.

   x <- array(1:60, dim = c(10, 2, 3))
   ld=length(dim(x))
   i=1 # i.e. the first row but can be a slice 1:5, whatever
   do.call(`[`, c(alist(x, i), alist(,)[rep(1,ld-1)], alist(drop=FALSE)))

Best,
Serguei.

>
> Rui Barradas
>
> Às 20:45 de 12/02/21, robin hankin escreveu:
>> Rui
>>
>>  > x <- array(runif(60), dim = c(10, 2, 3))
>>  > array(x[slice.index(x,1) %in% 1:5],c(5,dim(x)[-1]))
>>
>> (I don't see this on stackoverflow; should I post this there too?) 
>> Most of the magic package is devoted to handling arrays of arbitrary 
>> dimensions and this functionality might be good to include if anyone 
>> would find it useful.
>>
>> HTH
>>
>> Robin
>>
>>
>> <mailto:hankin.ro...@gmail.com>
>>
>>
>> On Sat, Feb 13, 2021 at 12:26 AM Rui Barradas > <mailto:ruipbarra...@sapo.pt>> wrote:
>>
>> Hello,
>>
>> This came up in this StackOverflow post [1].
>>
>> If x is an array with n dimensions, how to subset by just one 
>> dimension?
>> If n is known, it's simple, add the required number of commas in 
>> their
>> proper places.
>> But what if the user doesn't know the value of n?
>>
>> The example below has n = 3, and subsets by the 1st dim. The 
>> apply loop
>> solves the problem as expected but note that the index i has
>> length(i) > 1.
>>
>>
>> x <- array(1:60, dim = c(10, 2, 3))
>>
>> d <- 1L
>> i <- 1:5
>> apply(x, MARGIN = -d, '[', i)
>> x[i, , ]
>>
>>
>> If length(i) == 1, argument drop = FALSE doesn't work as I 
>> expected it
>> to work, only the other way does:
>>
>>
>> i <- 1L
>> apply(x, MARGIN = -d, '[', i, drop = FALSE)
>> x[i, , drop = FALSE]
>>
>>
>> What am I missing?
>>
>> [1]
>> https://stackoverflow.com/questions/66168564/is-there-a-native-r-synt
>> ax-to-extract-rows-of-an-array
>>
>> Thanks in advance,
>>
>> Rui Barradas
>>
>> __
>> R-devel@r-project.org <mailto:R-devel@r-project.org> mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
> __
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Re: [Rd] Unexpected behavior of '[' in an apply instruction

2021-02-12 Thread Sokol Serguei 

Le 12/02/2021 à 23:49, Sokol Serguei a écrit :

Le 12/02/2021 à 22:23, Rui Barradas a écrit :

Hello,

Yes, although there is an accepted solution, I believe you should 
post this solution there. It's a base R solution, what the question 
asks for.


And thanks, I would have never reminded myself of slice.index.


There is another approach -- produce a call to `[`() putting there 
"required number of commas in their proper places" programmatically. 
Even if it does not lead to a very readable expression, I think it 
merits to be mentioned.


  x <- array(1:60, dim = c(10, 2, 3))
  ld=length(dim(x))
  i=1 # i.e. the first row but can be a slice 1:5, whatever
  do.call(`[`, c(alist(x, i), alist(,)[rep(1,ld-1)], alist(drop=FALSE)))


Or slightly shorter:

  do.call(`[`, alist(x, i, ,drop=FALSE)[c(1,2,rep(3,ld-1),4)])



Best,
Serguei.



Rui Barradas

Às 20:45 de 12/02/21, robin hankin escreveu:

Rui

 > x <- array(runif(60), dim = c(10, 2, 3))
 > array(x[slice.index(x,1) %in% 1:5],c(5,dim(x)[-1]))

(I don't see this on stackoverflow; should I post this there too?)  
Most of the magic package is devoted to handling arrays of arbitrary 
dimensions and this functionality might be good to include if anyone 
would find it useful.


HTH

Robin





On Sat, Feb 13, 2021 at 12:26 AM Rui Barradas > wrote:


    Hello,

    This came up in this StackOverflow post [1].

    If x is an array with n dimensions, how to subset by just one 
dimension?
    If n is known, it's simple, add the required number of commas in 
their

    proper places.
    But what if the user doesn't know the value of n?

    The example below has n = 3, and subsets by the 1st dim. The 
apply loop

    solves the problem as expected but note that the index i has
    length(i) > 1.


    x <- array(1:60, dim = c(10, 2, 3))

    d <- 1L
    i <- 1:5
    apply(x, MARGIN = -d, '[', i)
    x[i, , ]


    If length(i) == 1, argument drop = FALSE doesn't work as I 
expected it

    to work, only the other way does:


    i <- 1L
    apply(x, MARGIN = -d, '[', i, drop = FALSE)
    x[i, , drop = FALSE]


    What am I missing?

    [1]
https://stackoverflow.com/questions/66168564/is-there-a-native-r-syntax-to-extract-rows-of-an-array 



    Thanks in advance,

    Rui Barradas

    __
    R-devel@r-project.org  mailing list
    https://stat.ethz.ch/mailman/listinfo/r-devel



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Re: [Rd] Unexpected behavior of '[' in an apply instruction

2021-02-12 Thread Sokol Serguei 

Le 12/02/2021 à 22:23, Rui Barradas a écrit :

Hello,

Yes, although there is an accepted solution, I believe you should post 
this solution there. It's a base R solution, what the question asks for.


And thanks, I would have never reminded myself of slice.index.


There is another approach -- produce a call to `[`() putting there 
"required number of commas in their proper places" programmatically. 
Even if it does not lead to a very readable expression, I think it 
merits to be mentioned.


  x <- array(1:60, dim = c(10, 2, 3))
  ld=length(dim(x))
  i=1 # i.e. the first row but can be a slice 1:5, whatever
  do.call(`[`, c(alist(x, i), alist(,)[rep(1,ld-1)], alist(drop=FALSE)))

Best,
Serguei.



Rui Barradas

Às 20:45 de 12/02/21, robin hankin escreveu:

Rui

 > x <- array(runif(60), dim = c(10, 2, 3))
 > array(x[slice.index(x,1) %in% 1:5],c(5,dim(x)[-1]))

(I don't see this on stackoverflow; should I post this there too?)  
Most of the magic package is devoted to handling arrays of arbitrary 
dimensions and this functionality might be good to include if anyone 
would find it useful.


HTH

Robin





On Sat, Feb 13, 2021 at 12:26 AM Rui Barradas > wrote:


    Hello,

    This came up in this StackOverflow post [1].

    If x is an array with n dimensions, how to subset by just one 
dimension?
    If n is known, it's simple, add the required number of commas in 
their

    proper places.
    But what if the user doesn't know the value of n?

    The example below has n = 3, and subsets by the 1st dim. The 
apply loop

    solves the problem as expected but note that the index i has
    length(i) > 1.


    x <- array(1:60, dim = c(10, 2, 3))

    d <- 1L
    i <- 1:5
    apply(x, MARGIN = -d, '[', i)
    x[i, , ]


    If length(i) == 1, argument drop = FALSE doesn't work as I 
expected it

    to work, only the other way does:


    i <- 1L
    apply(x, MARGIN = -d, '[', i, drop = FALSE)
    x[i, , drop = FALSE]


    What am I missing?

    [1]
https://stackoverflow.com/questions/66168564/is-there-a-native-r-syntax-to-extract-rows-of-an-array

    Thanks in advance,

    Rui Barradas

    __
    R-devel@r-project.org  mailing list
    https://stat.ethz.ch/mailman/listinfo/r-devel



__
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Re: [Rd] Unexpected behavior of '[' in an apply instruction

2021-02-12 Thread Rui Barradas 

Hello,

Yes, although there is an accepted solution, I believe you should post 
this solution there. It's a base R solution, what the question asks for.


And thanks, I would have never reminded myself of slice.index.

Rui Barradas

Às 20:45 de 12/02/21, robin hankin escreveu:

Rui

 > x <- array(runif(60), dim = c(10, 2, 3))
 > array(x[slice.index(x,1) %in% 1:5],c(5,dim(x)[-1]))

(I don't see this on stackoverflow; should I post this there too?)  Most 
of the magic package is devoted to handling arrays of arbitrary 
dimensions and this functionality might be good to include if anyone 
would find it useful.


HTH

Robin





On Sat, Feb 13, 2021 at 12:26 AM Rui Barradas > wrote:


Hello,

This came up in this StackOverflow post [1].

If x is an array with n dimensions, how to subset by just one dimension?
If n is known, it's simple, add the required number of commas in their
proper places.
But what if the user doesn't know the value of n?

The example below has n = 3, and subsets by the 1st dim. The apply loop
solves the problem as expected but note that the index i has
length(i) > 1.


x <- array(1:60, dim = c(10, 2, 3))

d <- 1L
i <- 1:5
apply(x, MARGIN = -d, '[', i)
x[i, , ]


If length(i) == 1, argument drop = FALSE doesn't work as I expected it
to work, only the other way does:


i <- 1L
apply(x, MARGIN = -d, '[', i, drop = FALSE)
x[i, , drop = FALSE]


What am I missing?

[1]

https://stackoverflow.com/questions/66168564/is-there-a-native-r-syntax-to-extract-rows-of-an-array

Thanks in advance,

Rui Barradas

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Re: [Rd] Unexpected behavior of '[' in an apply instruction

2021-02-12 Thread robin hankin 
Rui

> x <- array(runif(60), dim = c(10, 2, 3))
> array(x[slice.index(x,1) %in% 1:5],c(5,dim(x)[-1]))

(I don't see this on stackoverflow; should I post this there too?)  Most of
the magic package is devoted to handling arrays of arbitrary dimensions and
this functionality might be good to include if anyone would find it useful.

HTH

Robin





On Sat, Feb 13, 2021 at 12:26 AM Rui Barradas  wrote:

> Hello,
>
> This came up in this StackOverflow post [1].
>
> If x is an array with n dimensions, how to subset by just one dimension?
> If n is known, it's simple, add the required number of commas in their
> proper places.
> But what if the user doesn't know the value of n?
>
> The example below has n = 3, and subsets by the 1st dim. The apply loop
> solves the problem as expected but note that the index i has length(i) > 1.
>
>
> x <- array(1:60, dim = c(10, 2, 3))
>
> d <- 1L
> i <- 1:5
> apply(x, MARGIN = -d, '[', i)
> x[i, , ]
>
>
> If length(i) == 1, argument drop = FALSE doesn't work as I expected it
> to work, only the other way does:
>
>
> i <- 1L
> apply(x, MARGIN = -d, '[', i, drop = FALSE)
> x[i, , drop = FALSE]
>
>
> What am I missing?
>
> [1]
>
> https://stackoverflow.com/questions/66168564/is-there-a-native-r-syntax-to-extract-rows-of-an-array
>
> Thanks in advance,
>
> Rui Barradas
>
> __
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

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