How do I do a negative / nomatch / inverse search in data.table?

Question

What happens if I want to select all the rows in a data.table that do not contain a particular value in the key variable using binary search? By the way, what is the correct

Answer 1

The idiom is this:

DT[-DT["a", which=TRUE]]

   x y v
1: b 1 4
2: b 3 5
3: b 6 6
4: c 1 7
5: c 3 8
6: c 6 9

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Inspiration from:

• The mailing list posting Return Select/Join that does NOT match?
• The previous question non-joins with data.tables
• Matthew Dowle's answer to Porting set operations from R's data frames to data tables: How to identify duplicated rows?

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Update. New in v1.8.3 is not-join syntax. Farrel's first expectation (! rather than -) has been implemented :

DT[-DT["a",which=TRUE,nomatch=0],...]   # old idiom
DT[!"a",...]                            # same result, now preferred.

See the NEWS item for more detailed info and example.