Removing columns that are na or constant
Hello, Inline. Em 20-11-2012 22:03, Brian Feeny escreveu:
I have a dataset that has many columns which are NA or constant, and so I remove them like so:
same <- sapply(dataset, function(.col){
all(is.na(.col)) || all(.col[1L] == .col)
})
dataset <- dataset[!same]
This works GREAT (thanks to the r-users list archive I found this)
however, then when I do my data sampling like so:
testSize <- floor(nrow(x) * 10/100)
test <- sample(1:nrow(x), testSize)
train_data <- x[-test,]
test_data <- x[test, -1]
test_class <- x[test, 1]
It is now possible that test_data or train_data contain columns that are constants, however as one dataset they did not.
Suppose they do. If you now remove those columns from one of train_data or test_data, and not from the other, then their structures are no longer the same.
So the solution for me is to just re-run lines to remove all constants
Or write a function. I would have the function return the indices of the
good columns and then intersect the results for train_data and test_data.
notSame <- function(dataset){
same <- sapply(dataset, function(.col){
all(is.na(.col)) || all(.col[1L] == .col)
})
which(!same)
}
good1 <- notSame(train_data)
good2 <- notSame(test_data)
dataset <- dataset[intersect(good1, good2)]
Now you can sample from a "safe" subset of your dataset.
......not a problem, but is this normal? is this how I should be handling this in R? many models I am attempting to use (SVM, lda, etc) don't like if a column has all the same value....... so as a beginner, this is how I am handling it in R, but I am looking for someone to sanity check what I am doing is sound.
Only you can tell whether it's sound to eliminate variables from your analysis, and which ones. Hope this helps, Rui Barradas
Brian
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