Subsetting multiple columns of a data.table with the same column name

Question

Let say, for instance, I am having the following table: 

dt <- data.table(a = 1:3, b = 4:6, a = 7:9)

# dt

   a b a

1: 1 4 7

2: 2 5 8

3: 3 6 9

And I want to perform the subset of the data.table so that all columns with the name a get selected. The following code only provides the first match.

dt[, "a", with = F]

   a

1: 1

2: 2

3: 3

Answer 1

For achieving your goal output, you just have to pass a logical vector for selecting the columns.

library(data.table)

dt[, names(dt) == 'a', with = FALSE]

#   a a

#1: 1 7

#2: 2 8

#3: 3 9

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