[R] preserve class in apply function

[Rui Barradas]

Às 12:51 de 07/02/2023, Naresh Gurbuxani escreveu:
> 
>> 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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Hello,

The last form,


apply(mydf[,c("x", "y")], 1, function(row) {row["x"] + row["y"]})


is the right one. If your data has columns of a mix of classes, then the 
rows which are vectors are coerced to the greatest common denominator 
class.
 From ?c:


Details
The output type is determined from the highest type of the components in 
the hierarchy NULL < raw < logical < integer < double < complex < 
character < list < expression.



Also, since you have a data.frame the following is another possible way:


apply(mydf[c("x", "y")], 1, function(row) {row["x"] + row["y"]})


This doesn't work with matrices.

Hope this helps,

Rui Barradas