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Henrik Pärn

2018-Nov-29 08:20 UTC

[Rd] named arguments discouraged in `[.data.frame` and `[<-.data.frame`

Thanks Bill and Michael for taking the time to share your knowledge! 

As a further background to my question, here are two examples that I forgot to
include in my original post (reminded by Michael's answer). I swapped the i
and j arguments in `[.data.frame` and `[<-.data.frame`. With warnings, but
else without (?) problem. Using Bill's data:

`[.data.frame`(x = d, i = 1, j = 2)
# [1] 12

`[.data.frame`(x = d, j = 2, i = 1)
# [1] 12

And similar for `[<-.data.frame` :
`[<-.data.frame`(x = d, i = 1, j = 2, value = 1122)
`[<-.data.frame`(x = d, j = 2, i = 1, value = 12)

Because this seemed to work, I made the hasty conclusion that argument switching
_wasn't_ a problem for `[.data frame`, and that we could rely on exact
matching on tags. But apparently not: despite that `[.data.frame` and
`[<-.data.frame` are _not_ primitive functions, positional matching is done
there as well. Sometimes. At least when 'x' argument is not first, as
shown in Bill's examples. Obviously my "test" was insufficient...

Cheers,

Henrik



From: William Dunlap <wdunlap at tibco.com> 
Sent: Wednesday, November 28, 2018 9:10 PM
To: Henrik P?rn <henrik.parn at ntnu.no>
Cc: r-devel at r-project.org
Subject: Re: [Rd] named arguments discouraged in `[.data.frame` and
`[<-.data.frame`

They can get bitten in the last two lines of this example, where the 'x'
argument is not first:> d <- data.frame(C1=c(r1=11,r2=21,r3=31), C2=c(12,22,32))
> d[1,1:2]? ?C1 C2
r1 11 12> `[`(d,j=1:2,i=1)? ?C1 C2
r1 11 12
Warning message:
In `[.data.frame`(d, j = 1:2, i = 1) :
? named arguments other than 'drop' are
discouraged> `[`(j=1:2,d,i=1)Error in (1:2)[d, i = 1] : incorrect number of
dimensions> do.call("[", list(j=1:2, i=1, x=d))Error in 1:2[i = 1, x = list(C1 = c(11, 21, 31), C2 = c(12, 22, 32))] :
? incorrect number of dimensions

Bill Dunlap
TIBCO Software
wdunlap http://tibco.com


On Wed, Nov 28, 2018 at 11:30 AM Henrik P?rn <mailto:henrik.parn at
ntnu.no> wrote:
tl;dr:

Why are named arguments discouraged in `[.data.frame`, `[<-.data.frame` and
`[[.data.frame`?

(because this question is of the kind 'why is R designed like this?', I
though R-devel would be more appropriate than R-help)

#############################

Background:

Now and then students presents there fancy functions like this: 

myfancyfun(d,12,0.3,0.2,500,1000,FALSE,TRUE,FALSE,TRUE,FALSE)

Incomprehensible. Thus, I encourage them to use spaces and name arguments, _at
least_ when trying to communicate their code with others. Something like:

myfancyfun(data = d, n = 12, gamma = 0.3, prob = 0.2,
? ? ? ? ? ? ? ? ? ? ? size = 500, niter = 1000, model = FALSE,
? ? ? ? ? ? ? ? ? ? ?scale = TRUE, drop = FALSE, plot = TRUE, save = FALSE)


Then some overzealous students started to use named arguments everywhere.
E-v-e-r-y-w-h-e-r-e. Even in the most basic situation when indexing vectors (as
a subtle protest?), like:

vec <- 1:9

vec[i = 4]
`[`(x = vec, i = 4)

vec[[i = 4]]
`[[`(x = vec, i = 4)

vec[i = 4] <- 10
`[<-`(x = vec, i = 4, value = 10)

...or when indexing matrices:

m <- matrix(vec, ncol = 3)
m[i = 2, j = 2]
`[`(x = m, i = 2, j = 2)
# 5

m[i = 2, j = 2] <- 0
`[<-`(x = m, i = 2, j = 2, value = 0)

######

This practice indeed feels like overkill, but it didn't seem to hurt either.
Until they used it on data frames. Then suddenly warnings appeared that named
arguments are discouraged:

d <- data.frame(m)

d[[i = "X2"]]
# [1] 4 5 6
# Warning message:
# In `[[.data.frame`(d, i = "X2") :
#? named arguments other than 'exact' are discouraged

d[i = 2, j = 2]
# [1] 0
# Warning message:
# In `[.data.frame`(d, i = 2, j = 2) :
#? named arguments other than 'drop' are discouraged

d[i = 2, j = 2] <- 5
# Warning message:
# In `[<-.data.frame`(`*tmp*`, i = 2, j = 2, value = 5) :
#? named arguments are discouraged


##################################

Of course I could tell them "don't do it, it's overkill and not
common practice" or "it's just a warning, don't worry".
However, I assume the warnings are there for a good reason.

So how do I explain to the students that named arguments are actively
discouraged in `[.data.frame` and `[<-.data.frame`, but not in `[` and
`[<-`? When will they get bitten?

______________________________________________
mailto:R-devel at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Emil Bode

2018-Nov-29 09:48 UTC

head link

[Rd] named arguments discouraged in `[.data.frame` and `[<-.data.frame`

Well, the situation with `[.data.frame` (and [<-) is complicated by the fact
that the data.frame-method is not a primitive, but the generic IS.
I'm not sure about dispatch for primitive-generics, but I bet it's done
on the first argument (as with S3). Which means `[`(j=1:2,d,i=1) has nothing to
do with `[.data.frame`, as some internal code equivalent to something like
`[.integer` is called (`[.integer` is not an R-function, but I guess it's
implemented in the C-code for `[`)
And note that `[.data.frame`(j=1:2,d,i=1) does work (throws a warning, but
returns the right result), because then you're simply calling the direct
R-function, and matching by name is done.

But I think the main reason for the warning is forwards compatibility (and maybe
backwards?). As of this version, `[.data.frame`(x = d, j = 2, i = 1) works fine,
and `[.data.frame` is a regular R-function. But it's used a lot, I
wouldn't be surprised if some future R-version would implement it as a
primitive.
Without the warning, implementing [.data.frame as a primitive would involve a
LOT of issues where older code breaks. With the warning, we can make clear to
any users that calls like this one are undefined. They may work for now, but one
shouldn't rely on it. Which means only the "right" order may be
used, and then naming them is superfluous.

By the way, when trying some things I noticed something else, which I'll
send a separate mail about...

Cheers,
Emil 

?On 29/11/2018, 09:20, "R-devel on behalf of Henrik P?rn"
<r-devel-bounces at r-project.org on behalf of henrik.parn at ntnu.no>
wrote:

    Thanks Bill and Michael for taking the time to share your knowledge! 
    
    As a further background to my question, here are two examples that I forgot
to include in my original post (reminded by Michael's answer). I swapped the
i and j arguments in `[.data.frame` and `[<-.data.frame`. With warnings, but
else without (?) problem. Using Bill's data:
    
    `[.data.frame`(x = d, i = 1, j = 2)
    # [1] 12
    
    `[.data.frame`(x = d, j = 2, i = 1)
    # [1] 12
    
    And similar for `[<-.data.frame` :
    `[<-.data.frame`(x = d, i = 1, j = 2, value = 1122)
    `[<-.data.frame`(x = d, j = 2, i = 1, value = 12)
    
    Because this seemed to work, I made the hasty conclusion that argument
switching _wasn't_ a problem for `[.data frame`, and that we could rely on
exact matching on tags. But apparently not: despite that `[.data.frame` and
`[<-.data.frame` are _not_ primitive functions, positional matching is done
there as well. Sometimes. At least when 'x' argument is not first, as
shown in Bill's examples. Obviously my "test" was insufficient...
    
    Cheers,
    
    Henrik
    
    
    
    From: William Dunlap <wdunlap at tibco.com> 
    Sent: Wednesday, November 28, 2018 9:10 PM
    To: Henrik P?rn <henrik.parn at ntnu.no>
    Cc: r-devel at r-project.org
    Subject: Re: [Rd] named arguments discouraged in `[.data.frame` and
`[<-.data.frame`
    
    They can get bitten in the last two lines of this example, where the
'x' argument is not first:
    > d <- data.frame(C1=c(r1=11,r2=21,r3=31), C2=c(12,22,32))
    > d[1,1:2]
       C1 C2
    r1 11 12
    > `[`(d,j=1:2,i=1)
       C1 C2
    r1 11 12
    Warning message:
    In `[.data.frame`(d, j = 1:2, i = 1) :
      named arguments other than 'drop' are discouraged
    > `[`(j=1:2,d,i=1)
    Error in (1:2)[d, i = 1] : incorrect number of dimensions
    > do.call("[", list(j=1:2, i=1, x=d))
    Error in 1:2[i = 1, x = list(C1 = c(11, 21, 31), C2 = c(12, 22, 32))] :
      incorrect number of dimensions
    
    Bill Dunlap
    TIBCO Software
    wdunlap http://tibco.com
    
    
    On Wed, Nov 28, 2018 at 11:30 AM Henrik P?rn <mailto:henrik.parn at
ntnu.no> wrote:
    tl;dr:
    
    Why are named arguments discouraged in `[.data.frame`, `[<-.data.frame`
and `[[.data.frame`?
    
    (because this question is of the kind 'why is R designed like
this?', I though R-devel would be more appropriate than R-help)
    
    #############################
    
    Background:
    
    Now and then students presents there fancy functions like this: 
    
    myfancyfun(d,12,0.3,0.2,500,1000,FALSE,TRUE,FALSE,TRUE,FALSE)
    
    Incomprehensible. Thus, I encourage them to use spaces and name arguments,
_at least_ when trying to communicate their code with others. Something like:
    
    myfancyfun(data = d, n = 12, gamma = 0.3, prob = 0.2,
                          size = 500, niter = 1000, model = FALSE,
                         scale = TRUE, drop = FALSE, plot = TRUE, save = FALSE)
    
    
    Then some overzealous students started to use named arguments everywhere.
E-v-e-r-y-w-h-e-r-e. Even in the most basic situation when indexing vectors (as
a subtle protest?), like:
    
    vec <- 1:9
    
    vec[i = 4]
    `[`(x = vec, i = 4)
    
    vec[[i = 4]]
    `[[`(x = vec, i = 4)
    
    vec[i = 4] <- 10
    `[<-`(x = vec, i = 4, value = 10)
    
    ...or when indexing matrices:
    
    m <- matrix(vec, ncol = 3)
    m[i = 2, j = 2]
    `[`(x = m, i = 2, j = 2)
    # 5
    
    m[i = 2, j = 2] <- 0
    `[<-`(x = m, i = 2, j = 2, value = 0)
    
    ######
    
    This practice indeed feels like overkill, but it didn't seem to hurt
either. Until they used it on data frames. Then suddenly warnings appeared that
named arguments are discouraged:
    
    d <- data.frame(m)
    
    d[[i = "X2"]]
    # [1] 4 5 6
    # Warning message:
    # In `[[.data.frame`(d, i = "X2") :
    #  named arguments other than 'exact' are discouraged
    
    d[i = 2, j = 2]
    # [1] 0
    # Warning message:
    # In `[.data.frame`(d, i = 2, j = 2) :
    #  named arguments other than 'drop' are discouraged
    
    d[i = 2, j = 2] <- 5
    # Warning message:
    # In `[<-.data.frame`(`*tmp*`, i = 2, j = 2, value = 5) :
    #  named arguments are discouraged
    
    
    ##################################
    
    Of course I could tell them "don't do it, it's overkill and not
common practice" or "it's just a warning, don't worry".
However, I assume the warnings are there for a good reason.
    
    So how do I explain to the students that named arguments are actively
discouraged in `[.data.frame` and `[<-.data.frame`, but not in `[` and
`[<-`? When will they get bitten?
    
    ______________________________________________
    mailto:R-devel at r-project.org mailing list
    https://stat.ethz.ch/mailman/listinfo/r-devel
    ______________________________________________
    R-devel at r-project.org mailing list
    https://stat.ethz.ch/mailman/listinfo/r-devel

Henrik Pärn

2018-Nov-29 10:05 UTC

head link

[Rd] named arguments discouraged in `[.data.frame` and `[<-.data.frame`

Thanks Emil for your thorough answer. It really clarified a lot to me. And
revealed (even more of) my ignorance.
>-----Original Message-----
>From: Emil Bode <emil.bode at dans.knaw.nl>
>Sent: Thursday, November 29, 2018 10:48 AM
>To: Henrik P?rn <henrik.parn at ntnu.no>; r-devel at r-project.org
>Subject: Re: [Rd] named arguments discouraged in `[.data.frame` and `[<-
>.data.frame`
>
>Well, the situation with `[.data.frame` (and [<-) is complicated by the
fact that
>the data.frame-method is not a primitive, but the generic IS.
>I'm not sure about dispatch for primitive-generics, but I bet it's
done on the
>first argument (as with S3). Which means `[`(j=1:2,d,i=1) has nothing to do
>with `[.data.frame`, as some internal code equivalent to something like
>`[.integer` is called (`[.integer` is not an R-function, but I guess
it's
>implemented in the C-code for `[`)
>And note that `[.data.frame`(j=1:2,d,i=1) does work (throws a warning, but
>returns the right result), because then you're simply calling the direct
R-
>function, and matching by name is done.
>
>But I think the main reason for the warning is forwards compatibility (and
>maybe backwards?). As of this version, `[.data.frame`(x = d, j = 2, i = 1)
works
>fine, and `[.data.frame` is a regular R-function. But it's used a lot, I
wouldn't be
>surprised if some future R-version would implement it as a primitive.
>Without the warning, implementing [.data.frame as a primitive would involve
>a LOT of issues where older code breaks. With the warning, we can make clear
>to any users that calls like this one are undefined. They may work for now,
but
>one shouldn't rely on it. Which means only the "right" order
may be used, and
>then naming them is superfluous.
>
>By the way, when trying some things I noticed something else, which I'll
send
>a separate mail about...
>
>Cheers,
>Emil
>
>?On 29/11/2018, 09:20, "R-devel on behalf of Henrik P?rn"
<r-devel-
>bounces at r-project.org on behalf of henrik.parn at ntnu.no> wrote:
>
>    Thanks Bill and Michael for taking the time to share your knowledge!
>
>    As a further background to my question, here are two examples that I
>forgot to include in my original post (reminded by Michael's answer). I
>swapped the i and j arguments in `[.data.frame` and `[<-.data.frame`.
With
>warnings, but else without (?) problem. Using Bill's data:
>
>    `[.data.frame`(x = d, i = 1, j = 2)
>    # [1] 12
>
>    `[.data.frame`(x = d, j = 2, i = 1)
>    # [1] 12
>
>    And similar for `[<-.data.frame` :
>    `[<-.data.frame`(x = d, i = 1, j = 2, value = 1122)
>    `[<-.data.frame`(x = d, j = 2, i = 1, value = 12)
>
>    Because this seemed to work, I made the hasty conclusion that argument
>switching _wasn't_ a problem for `[.data frame`, and that we could rely
on
>exact matching on tags. But apparently not: despite that `[.data.frame` and
>`[<-.data.frame` are _not_ primitive functions, positional matching is
done
>there as well. Sometimes. At least when 'x' argument is not first,
as shown in
>Bill's examples. Obviously my "test" was insufficient...
>
>    Cheers,
>
>    Henrik
>
>
>
>    From: William Dunlap <wdunlap at tibco.com>
>    Sent: Wednesday, November 28, 2018 9:10 PM
>    To: Henrik P?rn <henrik.parn at ntnu.no>
>    Cc: r-devel at r-project.org
>    Subject: Re: [Rd] named arguments discouraged in `[.data.frame` and
`[<-
>.data.frame`
>
>    They can get bitten in the last two lines of this example, where the
'x'
>argument is not first:
>    > d <- data.frame(C1=c(r1=11,r2=21,r3=31), C2=c(12,22,32))
>    > d[1,1:2]
>       C1 C2
>    r1 11 12
>    > `[`(d,j=1:2,i=1)
>       C1 C2
>    r1 11 12
>    Warning message:
>    In `[.data.frame`(d, j = 1:2, i = 1) :
>      named arguments other than 'drop' are discouraged
>    > `[`(j=1:2,d,i=1)
>    Error in (1:2)[d, i = 1] : incorrect number of dimensions
>    > do.call("[", list(j=1:2, i=1, x=d))
>    Error in 1:2[i = 1, x = list(C1 = c(11, 21, 31), C2 = c(12, 22, 32))] :
>      incorrect number of dimensions
>
>    Bill Dunlap
>    TIBCO Software
>    wdunlap http://tibco.com
>
>
>    On Wed, Nov 28, 2018 at 11:30 AM Henrik P?rn
><mailto:henrik.parn at ntnu.no> wrote:
>    tl;dr:
>
>    Why are named arguments discouraged in `[.data.frame`,
`[<-.data.frame`
>and `[[.data.frame`?
>
>    (because this question is of the kind 'why is R designed like
this?', I though
>R-devel would be more appropriate than R-help)
>
>    #############################
>
>    Background:
>
>    Now and then students presents there fancy functions like this:
>
>    myfancyfun(d,12,0.3,0.2,500,1000,FALSE,TRUE,FALSE,TRUE,FALSE)
>
>    Incomprehensible. Thus, I encourage them to use spaces and name
>arguments, _at least_ when trying to communicate their code with others.
>Something like:
>
>    myfancyfun(data = d, n = 12, gamma = 0.3, prob = 0.2,
>                          size = 500, niter = 1000, model = FALSE,
>                         scale = TRUE, drop = FALSE, plot = TRUE, save =
FALSE)
>
>
>    Then some overzealous students started to use named arguments
>everywhere. E-v-e-r-y-w-h-e-r-e. Even in the most basic situation when
>indexing vectors (as a subtle protest?), like:
>
>    vec <- 1:9
>
>    vec[i = 4]
>    `[`(x = vec, i = 4)
>
>    vec[[i = 4]]
>    `[[`(x = vec, i = 4)
>
>    vec[i = 4] <- 10
>    `[<-`(x = vec, i = 4, value = 10)
>
>    ...or when indexing matrices:
>
>    m <- matrix(vec, ncol = 3)
>    m[i = 2, j = 2]
>    `[`(x = m, i = 2, j = 2)
>    # 5
>
>    m[i = 2, j = 2] <- 0
>    `[<-`(x = m, i = 2, j = 2, value = 0)
>
>    ######
>
>    This practice indeed feels like overkill, but it didn't seem to hurt
either. Until
>they used it on data frames. Then suddenly warnings appeared that named
>arguments are discouraged:
>
>    d <- data.frame(m)
>
>    d[[i = "X2"]]
>    # [1] 4 5 6
>    # Warning message:
>    # In `[[.data.frame`(d, i = "X2") :
>    #  named arguments other than 'exact' are discouraged
>
>    d[i = 2, j = 2]
>    # [1] 0
>    # Warning message:
>    # In `[.data.frame`(d, i = 2, j = 2) :
>    #  named arguments other than 'drop' are discouraged
>
>    d[i = 2, j = 2] <- 5
>    # Warning message:
>    # In `[<-.data.frame`(`*tmp*`, i = 2, j = 2, value = 5) :
>    #  named arguments are discouraged
>
>
>    ##################################
>
>    Of course I could tell them "don't do it, it's overkill and
not common
>practice" or "it's just a warning, don't worry".
However, I assume the warnings
>are there for a good reason.
>
>    So how do I explain to the students that named arguments are actively
>discouraged in `[.data.frame` and `[<-.data.frame`, but not in `[` and
`[<-`?
>When will they get bitten?
>
>    ______________________________________________
>    mailto:R-devel at r-project.org mailing list
>    https://stat.ethz.ch/mailman/listinfo/r-devel
>    ______________________________________________
>    R-devel at r-project.org mailing list
>    https://stat.ethz.ch/mailman/listinfo/r-devel
>

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