0a4a5b36cc
* Additional .gitignore entries * Merge a bunch of small articles about system tables into single one * Merge a bunch of small articles about formats into single one * Adapt table with formats to English docs too * Add SPb meetup link to main page * Move Utilities out of top level of docs (the location is probably not yet final) + translate couple articles * Merge MacOS.md into build_osx.md * Move Data types higher in ToC * Publish changelog on website alongside documentation * Few fixes for en/table_engines/file.md * Use smaller header sizes in changelogs * Group up table engines inside ToC * Move table engines out of top level too * Specificy in ToC that query language is SQL based. Thats a bit excessive, but catches eye. * Move stuff that is part of query language into respective folder * Move table functions lower in ToC * Lost redirects.txt update * Do not rely on comments in yaml + fix few ru titles * Extract major parts of queries.md into separate articles * queries.md has been supposed to be removed * Fix weird translation * Fix a bunch of links * There is only table of contents left * "Query language" is actually part of SQL abbreviation * Change filename in README.md too * fix mistype
3.8 KiB
Higher-order functions
-> operator, lambda(params, expr) function
Allows describing a lambda function for passing to a higher-order function. The left side of the arrow has a formal parameter, which is any ID, or multiple formal parameters – any IDs in a tuple. The right side of the arrow has an expression that can use these formal parameters, as well as any table columns.
Examples: x -> 2 * x, str -> str != Referer.
Higher-order functions can only accept lambda functions as their functional argument.
A lambda function that accepts multiple arguments can be passed to a higher-order function. In this case, the higher-order function is passed several arrays of identical length that these arguments will correspond to.
For all functions other than 'arrayMap' and 'arrayFilter', the first argument (the lambda function) can be omitted. In this case, identical mapping is assumed.
arrayMap(func, arr1, ...)
Returns an array obtained from the original application of the 'func' function to each element in the 'arr' array.
arrayFilter(func, arr1, ...)
Returns an array containing only the elements in 'arr1' for which 'func' returns something other than 0.
Examples:
SELECT arrayFilter(x -> x LIKE '%World%', ['Hello', 'abc World']) AS res
┌─res───────────┐
│ ['abc World'] │
└───────────────┘
SELECT
arrayFilter(
(i, x) -> x LIKE '%World%',
arrayEnumerate(arr),
['Hello', 'abc World'] AS arr)
AS res
┌─res─┐
│ [2] │
└─────┘
arrayCount([func,] arr1, ...)
Returns the number of elements in the arr array for which func returns something other than 0. If 'func' is not specified, it returns the number of non-zero elements in the array.
arrayExists([func,] arr1, ...)
Returns 1 if there is at least one element in 'arr' for which 'func' returns something other than 0. Otherwise, it returns 0.
arrayAll([func,] arr1, ...)
Returns 1 if 'func' returns something other than 0 for all the elements in 'arr'. Otherwise, it returns 0.
arraySum([func,] arr1, ...)
Returns the sum of the 'func' values. If the function is omitted, it just returns the sum of the array elements.
arrayFirst(func, arr1, ...)
Returns the first element in the 'arr1' array for which 'func' returns something other than 0.
arrayFirstIndex(func, arr1, ...)
Returns the index of the first element in the 'arr1' array for which 'func' returns something other than 0.
arrayCumSum([func,] arr1, ...)
Returns an array of partial sums of elements in the source array (a running sum). If the func function is specified, then the values of the array elements are converted by this function before summing.
Example:
SELECT arrayCumSum([1, 1, 1, 1]) AS res
┌─res──────────┐
│ [1, 2, 3, 4] │
└──────────────┘
arraySort([func,] arr1, ...)
Returns an array as result of sorting the elements of arr1 in ascending order. If the func function is specified, sorting order is determined by the result of the function func applied to the elements of array (arrays)
The Schwartzian transform is used to impove sorting efficiency.
Example:
SELECT arraySort((x, y) -> y, ['hello', 'world'], [2, 1]);
┌─res────────────────┐
│ ['world', 'hello'] │
└────────────────────┘
arrayReverseSort([func,] arr1, ...)
Returns an array as result of sorting the elements of arr1 in descending order. If the func function is specified, sorting order is determined by the result of the function func applied to the elements of array (arrays)