R devel - Aug 2015 - Weird issue when iterating through dates

Thanks G?bor,
I thought there was some mistake in my logic on how casting works in R
and wanted to be sure.

Just a quick question: what's the difference between  `[.Date` and 
`[[.Date`?
Is it supposed to be the method for accessing the value right?

Thanks again for your help,
Cheers,
Luca

On Thu, Aug 6, 2015 at 10:10 AM, G?bor Cs?rdi <csardi.gabor at gmail.com>
wrote:
> Date has a `[.Date` method and also `[[.Date`, but it looks like a for
> loop does not consider the class of the object you are iterating over,
> so these are ignored and the internal representation is used.
>
> I think this is a bug, at least in the documentation of ?"for".
>
> Interestingly, lapply and co. do consider the class:
>
> invisible(lapply(seq(d1, d2, by = 1), print))
>
> works as you would expect. (The invisible() is to suppress printing
> the return value.)
>
> Gabor
>
> On Thu, Aug 6, 2015 at 3:24 AM, Luca Cerone <luca.cerone at
gmail.com> wrote:
>> Dear all,
>> I am experiencing a weird issue when iterating through dates in R
>> (3.1.2 and 3.2.1 on 64bit linux machines)
>>
>> I am bit surprised about the behaviour of this snippet of code:
>>
>> d1 <- as.Date('2015-01-01')
>> d2 <- as.Date('2015-01-31')
>>
>> for ( dt in seq(d1,d2, by=1) ) {
>>   dt <- as.character(dt)
>>   print(dt)
>> }
>>
>> for ( dt in as.character(seq(d1,d2, by=1)) ) {
>>   print(dt)
>> }
>>
>> I can't find a good explanation why the first for loop would
convert
>> to string the numeric interpretation
>> of the dates while the second one correctly (at least in my
>> intentions) prints the dates as string.
>>
>> I am sure that it is not a bug in R but I would like to understand why
>> I am getting different outputs from the two for loops.
>>
>> Thanks a lot in advance for your help!
>>
>> Cheers,
>> Luca
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel

On Thu, Aug 6, 2015 at 6:30 AM, Luca Cerone <luca.cerone at gmail.com>
wrote:
[...]
> Just a quick question: what's the difference between  `[.Date` and 
`[[.Date`?
> Is it supposed to be the method for accessing the value right?
For Dates and atomic vectors in general they are the same, but in
general they are two different operators that behave differently on
some data types. E.g. on lists [ selects a sub-list and [[ selects a
single element.

Gabor

[...]

>> Just a quick question: what's the difference between  `[.Date` and
`[[.Date`?
>> Is it supposed to be the method for accessing the value right?
>
>For Dates and atomic vectors in general they are the same, but ...
Even for atomic vectors with names they are not quite the same
    > c(One=1, Two=2)[[2]]
    [1] 2
    > c(One=1, Two=2)[2]
    Two
      2
(and [[ will only return 1 item, unlike [).


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Thu, Aug 6, 2015 at 5:36 AM, G?bor Cs?rdi <csardi.gabor at gmail.com>
wrote:
> On Thu, Aug 6, 2015 at 6:30 AM, Luca Cerone <luca.cerone at
gmail.com> wrote:
> [...]
> > Just a quick question: what's the difference between  `[.Date` and
> `[[.Date`?
> > Is it supposed to be the method for accessing the value right?
>
> For Dates and atomic vectors in general they are the same, but in
> general they are two different operators that behave differently on
> some data types. E.g. on lists [ selects a sub-list and [[ selects a
> single element.
>
> Gabor
>
> [...]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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