Reduce operator

Reduce

Syntax

reduce <var> = <operator> [ (<var>) ] [ , ... ];

TypeQL supports the following reduce operators:

count — total number of answers, or, when used with a variable, number of distinct values of the variable,
max — the maximum value of the variable,
min — the minimum value of the variable,
mean — the arithmetic mean of the values of the variable,
median — the median value of the variable,
std — the sample standard deviation of the values of the variable,
sum — the sum of the values of the variable.

Examples

Count the number of logins since <datetime>:

match
  $user isa user, has last-login >= <datetime>;
reduce $logins = count;

Get disk usage statistics of the files:

match
  $file isa file, has size-kb $s;
reduce $total = sum($s), $mean = mean($s), $max = max($s);

Grouping

When groupby is used within a reduce, the answer stream is subdivided into groups based on the value of the grouping variable. The reduction is then performed separately within each such group. The output of a reduce with groupby is a stream of rows, one for each value of the grouping variable.

Syntax

reduce <var> = <operator> [ (<var>) ] [ , ... ] groupby <var>;

Example

Get the number of users per country:

match
  $user isa user;
  $country isa country;
  {
    located($user, $country);
  } or {
    located($user, $place);
    located($place, $country);
  };
reduce $logins = count groupby $country;