[R] Antwort: RE: Antwort: Fw: Re: Subscripting problem with is.na()
Duncan Murdoch
murdoch.duncan at gmail.com
Mon Jun 27 13:57:06 CEST 2016
On 27/06/2016 7:43 AM, G.Maubach at weinwolf.de wrote:
> Hi Petr,
>
> many thanks for your reply and the examples.
>
> My subscripting problems drive me nuts.
>
> I have understood that dataset[variable] is semantically identical to
> dataset[, variable] cause dataset[variable] takes all cases because no
> other subscripts are given.
>
> Where can I lookup the rules when to use the comma and when not?
I don't think you'll find an explicit list of rules in the R
documentation. It does imply the rules, however, by saying that a data
frame is a list which can be indexed as a matrix.
So if you want to treat your dataset as a list of columns, use single
component list indexing: dataset[columnname] to give another list,
dataset[[columnname]] to extract the column as a vector.
If you want to treat it as a matrix of values, use two indices:
dataset[row, column]
to extract the entry (or entries, if row or column contains more than
one value).
Duncan Murdoch
>
> Kind regards
>
> Georg
>
>
>
>
>
> Von: PIKAL Petr <petr.pikal at precheza.cz>
> An: "G.Maubach at weinwolf.de" <G.Maubach at weinwolf.de>,
> Kopie: "r-help at r-project.org" <r-help at r-project.org>
> Datum: 27.06.2016 11:03
> Betreff: RE: [R] Antwort: Fw: Re: Subscripting problem with
> is.na()
>
>
>
> Hi
>
> see in line
>
>> -----Original Message-----
>> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of
>> G.Maubach at weinwolf.de
>> Sent: Monday, June 27, 2016 10:45 AM
>> To: David L Carlson <dcarlson at tamu.edu>; Bert Gunter
>> <bgunter.4567 at gmail.com>
>> Cc: r-help at r-project.org
>> Subject: [R] Antwort: Fw: Re: Subscripting problem with is.na()
>>
>> Hi David,
>> Hi Bert,
>>
>> many thanks for the valuable discussion on NA in R (please see extract
>> below). I follow your arguments leaving NA as they are for most of the
>> time. In special occasions however I want to replace the NA with another
>> value. To preserve the newly acquired knowledge for me I wrote this
>> function:
>>
>> -- cut --
>> t_replace_na <- function(dataset, variable, value) {
>> if(inherits(dataset[[variable]], "factor") == TRUE) {
>> dataset[variable] <- as.character(dataset[variable])
>> print(class(dataset[variable]))
>> dataset[, variable][is.na(dataset[, variable])] <- value
>> dataset[variable] <- as.factor(dataset[variable])
>> print(class(dataset[variable]))
>> } else {
>> dataset[, variable][is.na(dataset[, variable])] <- value
>> }
>> return(dataset)
>> }
>>
>
> <snip>
>
>> class(ds_test[, "c"])
>> test_class(ds_test, "c")
>> warning("'c' should be factor NOT data.frame.
>> In addition data.frame != factor")
>> -- cut --
>>
>> Why do I get different results for the same function if it is inside or
>> outside my own function definition?
>
> Because you still are missing the way how to subscript data frames.
>
> test_class <- function(dataset, variable) {
> if(inherits(dataset[, variable], "factor") == TRUE) {
> return(c(class(dataset[,variable]), TRUE))
> #### ^^^^
> } else {
> return(c(class(dataset[,variable]), FALSE))
> ###### ^^^^
> }
> }
>
>> test_class(ds_test, "a")
> [1] "numeric" "FALSE"
>> test_class(ds_test, "c")
> [1] "factor" "TRUE"
>>
>
> If you properly arrange commas in your function you get desired result
>
> p_replace_na <- function(dataset, variable, value) {
> if(inherits(dataset[,variable], "factor") == TRUE) {
> dataset[,variable] <- as.character(dataset[,variable])
> print(class(dataset[,variable]))
> dataset[, variable][is.na(dataset[, variable])] <- value
> dataset[, variable] <- as.factor(dataset[, variable])
> print(class(dataset[, variable]))
> } else {
> dataset[, variable][is.na(dataset[, variable])] <- value
> }
> return(dataset)
> }
>
>> p_replace_na(ds_test, "c", value = -3)
> [1] "character"
> [1] "factor"
> a b c
> 1 1 NA A
> 2 NA NA b
> 3 2 NA -3
>
>> t_replace_na(ds_test, "c", value = -3)
> [1] "data.frame"
> Error in sort.list(y) : 'x' must be atomic for 'sort.list'
> Have you called 'sort' on a list?
>>
>
> Cheers
> Petr
>
>
>
>>
>> Kind regards
>>
>> Georg
>>
>> --------------------------------
>>
>>> Gesendet: Donnerstag, 23. Juni 2016 um 21:14 Uhr
>>> Von: "David L Carlson" <dcarlson at tamu.edu>
>>> An: "Bert Gunter" <bgunter.4567 at gmail.com>
>>> Cc: "R Help" <r-help at r-project.org>
>>> Betreff: Re: [R] Subscripting problem with is.na()
>>>
>>> Good point. I did not think about factors. Also your example raises
>> another issue since column c is logical, but gets silently converted to
>> numeric. This would seem to get the job done assuming the conversion is
>> intended for numeric columns only:
>>>
>>>> test <- data.frame(a=c(1,NA,2), b = c("A","b",NA), c= rep(NA,3))
>>>> sapply(test, class)
>>> a b c
>>> "numeric" "factor" "logical"
>>>> num <- sapply(test, is.numeric)
>>>> test[, num][is.na(test[, num])] <- 0
>>>> test
>>> a b c
>>> 1 1 A NA
>>> 2 0 b NA
>>> 3 2 <NA> NA
>>>
>>> David C
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>> guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
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