[R] preserve class in apply function

[Naresh Gurbuxani]

> 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