sort

Operator

  sort — sort values

Synopsis

sort [-r] [-nulls first|last] [<expr> [, <expr> ...]]

Description

The sort operator sorts its input by reading all values until the end of input, sorting the values according to the provided sort expression(s), and emitting the values in the sorted order.

By default, the sort order is ascending, from lowest value to highest. If the -r flag is provided, the sort order is descending.

Zed follows the SQL convention that, by default, null values appear last in either case of ascending or descending sort. This can be overridden by specifying -nulls first.

If not all data fits in memory, values are spilled to temporary storage and sorted with an external merge sort.

The sort expressions act as primary key, secondary key, and so forth.

If no sort expression is provided, a sort key is guessed based on heuristics applied to the values present. The heuristic examines the first input record and finds the first field in left-to-right order that is an integer, or if no integer field is found, the first field that is floating point. If no such numeric field is found, sort finds the first field in left-to-right order that is not of the time data type. Note that there are some cases (such as the output of a grouped aggregation performed on heterogeneous data) where the first input record to sort may vary even when the same query is executed repeatedly against the same data. If you require a query to show deterministic output on repeated execution, an explicit field list must be provided.

Note that a total order is defined over the space of all Zed values even between values of different types so sort order is always well-defined even when comparing heterogeneously typed values.

TBD: document the definition of the total order

Examples

A simple sort with a null

echo '2 null 1 3' | zq -z 'sort this' -

=>

1
2
3
null

With no sort expression, sort will sort by this for non-records

echo '2 null 1 3' | zq -z sort -

=>

1
2
3
null

The "nulls last" default may be overridden

echo '2 null 1 3' | zq -z 'sort -nulls first' -

=>

null
1
2
3

With no sort expression, sort will find a numeric key

echo '{s:"bar",k:2}{s:"bar",k:3}{s:"foo",k:1}' | zq -z sort -

=>

{s:"foo",k:1}
{s:"bar",k:2}
{s:"bar",k:3}

It's best practice to provide the sort key

echo '{s:"bar",k:2}{s:"bar",k:3}{s:"foo",k:1}' | zq -z 'sort k' -

=>

{s:"foo",k:1}
{s:"bar",k:2}
{s:"bar",k:3}

Sort with a secondary key

echo '{s:"bar",k:2}{s:"bar",k:3}{s:"foo",k:2}' | zq -z 'sort k,s' -

=>

{s:"bar",k:2}
{s:"foo",k:2}
{s:"bar",k:3}

Sort with an expression

echo '{s:"sum 2",x:2,y:0}{s:"sum 3",x:1,y:2}{s:"sum 0",x:-1,y:-1}' | zq -z 'sort x+y' -

=>

{s:"sum 0",x:-1,y:-1}
{s:"sum 2",x:2,y:0}
{s:"sum 3",x:1,y:2}