[R] preserve class in apply function

[@vi@e@gross m@iii@g oii gm@ii@com]

Naresh,

This is a common case where the answer to a question is to ask the right question.

Your question was how to make apply work. My question is how can you get the functionality you want done in some version of R.

Apply is a tool and it is only one of many tools and may be the wrong one for your task. 

For a data.frame there can be lots of tools you may investigate both in vase R and add-on packages like dplyr in the tidyverse.

As has been pointed out, a side-effect of apply is to make a matrix and R automagically figures out what the most specific kind of data type it can handle.

So solutions range from not including any columns that are not numeric, if that makes sense, to accepting they are all going to be of type character and in the function you apply, convert them individually back to what you want.

One straightforward solution is to make a loop indexed to the number of rows in your data.frame and process the variables in each row using [] notation. Not fast, but you see what you have. 

Another is functions like pmap() in the purr package. Yet another might be the rowwise() function in the dplyr package.

It depends on what you want to do. Note with multiple columns, sometimes your function may need to use a ... to receive them.
-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Naresh Gurbuxani
Sent: Tuesday, February 7, 2023 3:29 PM
To: PIKAL Petr <petr.pikal using precheza.cz>
Cc: r-help using r-project.org
Subject: Re: [R] preserve class in apply function

Thanks for all the responses.  I need to use some text columns to determine method applied to numeric columns. 

Split seems to be the way to go.

Sent from my iPhone

> On Feb 7, 2023, at 8:31 AM, PIKAL Petr <petr.pikal using precheza.cz> wrote:
> 
> Hi Naresh
> 
> If you wanted to automate the function a bit you can use sapply to 
> find numeric columns ind <- sapply(mydf, is.numeric)
> 
> and use it in apply construct
> apply(mydf[,ind], 1, function(row) sum(row)) [1]  2.13002569  
> 0.63305300  1.48420429  0.13523859  1.17515873 -0.98531131 [7]  
> 0.47044467  0.23914494  0.26504430  0.02037657
> 
> Cheers
> Petr
> 
>> -----Original Message-----
>> From: R-help <r-help-bounces using r-project.org> On Behalf Of Naresh 
>> Gurbuxani
>> Sent: Tuesday, February 7, 2023 1:52 PM
>> To: r-help using r-project.org
>> Subject: [R] preserve class in apply function
>> 
>> 
>>> Consider a data.frame whose different columns have numeric, 
>>> character, and factor data.  In apply function, R seems to pass all 
>>> elements of a row as character.  Is it possible to preserve numeric class?
>>> 
>>>> mydf <- data.frame(x = rnorm(10), y = runif(10)) apply(mydf, 1, 
>>>> function(row) {row["x"] + row["y"]})
>>> [1]  0.60150197 -0.74201827  0.80476392 -0.59729280 -0.02980335
>> 0.31351909
>>> [7] -0.63575990  0.22670658  0.55696314  0.39587314
>>>> mydf[, "z"] <- sample(letters[1:3], 10, replace = TRUE) apply(mydf, 
>>>> 1, function(row) {row["x"] + row["y"]})
>>> Error in row["x"] + row["y"] (from #1) : non-numeric argument to 
>>> binary
>> operator
>>>> apply(mydf, 1, function(row) {as.numeric(row["x"]) +
>> as.numeric(row["y"])})
>>> [1]  0.60150194 -0.74201826  0.80476394 -0.59729282 -0.02980338
>> 0.31351912
>>> [7] -0.63575991  0.22670663  0.55696309  0.39587311
>>>> apply(mydf[,c("x", "y")], 1, function(row) {row["x"] + row["y"]})
>>> [1]  0.60150197 -0.74201827  0.80476392 -0.59729280 -0.02980335
>> 0.31351909
>>> [7] -0.63575990  0.22670658  0.55696314  0.39587314
>> 
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.