2

How can I remove every column that meets a specific condition from a specific row? In my case remove each column with =="-" in the first row.

I want to do it completely inside [ ] without copying the data in memory, and if possible avoiding an external function.

mtcars[1,c(2,4,6)] <- "-"
dt <- data.table(mtcars)

didn't work:

temp[,.SDcols := function(x) x[1]!="-"]
temp[,.SD:= .SDcols = (function(x) x[1]!="-")]

works but copies the data:

temp[ , .SD, .SDcols = function(x) x[1]!="-"]

there are other posts about this topic but my question is different because none of these posts show how to subset before looking for a condition inside the [ ]

delete column in data.table in R based on condition

Removing multiple columns from R data.table with parameter for columns to remove

Improve this question

2 Answers 2

Reset to default
2

You could drop the columns containing "-" in the first rows by reference as follows:

dt[, which(c(dt[1]=="-")) := NULL]
Improve this answer
Sign up to request clarification or add additional context in comments.

Comments

1

How about this?

 dt[,dt[1]!="-", with=FALSE]
Improve this answer

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.