[R] Subscripting problem with is.na()

[Ivan Calandra]

My statement "Using a single bracket '[' on a data.frame does the same 
as for matrices: you need to specify rows and columns" was not correct.


When you use a single bracket on a list with only one argument in 
between, then R extracts "elements", i.e. columns in the case of a 
data.frame. This explains your errors.

But it is possible to use a single bracket on a data.frame with 2 
arguments (rows, columns) separated by a comma, as with matrices. This 
is the solution you received.

Ivan


--
Ivan Calandra, PhD
Scientific Mediator
University of Reims Champagne-Ardenne
GEGENAA - EA 3795
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+33(0)3 26 77 36 89
ivan.calandra at univ-reims.fr
--
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Le 23/06/2016 à 16:27, Ivan Calandra a écrit :
> Dear Georg,
>
> You need to learn a bit more about the subsetting methods, depending 
> on the object structure you're trying to subset.
>
> More specifically, when you run this: ds_test[is.na(ds_test$var1)]
> you get this error: "Error in `[.data.frame`(ds_test, 
> is.na(ds_test$var1)) : undefined columns selected"
>
> This means that R does not understand which column you're trying to 
> select. But you're actually trying to select rows.
>
> Using a single bracket '[' on a data.frame does the same as for 
> matrices: you need to specify rows and columns, like this:
> ds_test[is.na(ds_test$var1), ] ## notice the last comma
> ds_test[is.na(ds_test$var1), ] <- 0 ## works on all columns because 
> you didn't specify any after the comma
>
> If you want it only for "var1", then you need to specify the column:
> ds_test[is.na(ds_test$var1), "var1"] <- 0
>
> It's the same problem with your 2nd and 4th tries (4th one has other 
> problems). Your 3rd try does not change ds_test at all.
>
> HTH,
> Ivan
>
> -- 
> Ivan Calandra, PhD
> Scientific Mediator
> University of Reims Champagne-Ardenne
> GEGENAA - EA 3795
> CREA - 2 esplanade Roland Garros
> 51100 Reims, France
> +33(0)3 26 77 36 89
> ivan.calandra at univ-reims.fr
> -- 
> https://www.researchgate.net/profile/Ivan_Calandra
> https://publons.com/author/705639/
>
> Le 23/06/2016 à 15:57, G.Maubach at weinwolf.de a écrit :
>> Hi All,
>>
>> I would like to recode my NAs to 0. Using a single vector everything is
>> fine.
>>
>> But if I use a data.frame things go wrong:
>>
>> -- cut --
>>
>> var1 <- c(1:3, NA, 5:7, NA, 9:10)
>> var2 <- c(1:3, NA, 5:7, NA, 9:10)
>> ds_test <-
>>    data.frame(var1, var2)
>>
>> test <- var1
>> test[is.na(test)] <- 0
>> test  # NA recoded OK
>>
>> # First try
>> ds_test[is.na(ds_test$var1)] <- 0  # duplicate subscripts WRONG
>>
>> # Second try
>> ds_test[is.na("var1")] <- 0
>> ds_test$var1  # not recoded WRONG
>>
>> # Third try: to me the most intuitive approach
>> is.na(ds_test["var1"]) <- 0  # attempt to select less than one 
>> element in
>> integerOneIndex WRONG
>>
>> # Fourth try
>> ds_test[is.na(var1)] <- 0  # duplicate subscripts for columns WRONG
>>
>> -- cut --
>>   How can I do it correctly?
>>
>> Where could I have found something about it?
>>
>> Kind regards
>>
>> Georg
>>
>> ______________________________________________
>> R-help at r-project.org 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.
>>
>
> ______________________________________________
> R-help at r-project.org 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.
>