Next Previous Up Contents
Next: stats
Up: Processing Filters
Previous: sort

#### 6.1.32 `sorthead`

Usage:

       sorthead [-tail] [-down] [-nullsfirst] <nrows> <key-list>

Performs a sort on the table according to the value of one or more algebraic expressions, retaining only `<nrows>` rows at the head of the resulting sorted table. The sort key expressions appear, as separate (space-separated) words, in `<key-list>`; sorting is done on the first expression first, but if that results in a tie then the second one is used, and so on. Each expression must evaluate to a type that it makes sense to sort, for instance numeric.

If the `-tail` flag is used, then the last `<nrows>` rows rather than the first ones are retained.

If the `-down` flag is used the sort order is descending rather than ascending.

Blank entries are by default considered to come at the end of the collation sequence, but if the `-nullsfirst` flag is given then they are considered to come at the start instead.

This filter is functionally equivalent to using `sort` followed by `head`, but it can be done in one pass and is usually cheaper on memory and faster, as long as `<nrows>` is significantly lower than the size of the table.

Syntax for the `<key-list>` argument is described in Section 10.

Next Previous Up Contents
Next: stats
Up: Processing Filters
Previous: sort

STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk