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68 lines
2.6 KiB
ReStructuredText
68 lines
2.6 KiB
ReStructuredText
Higher-order functions
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-----------------------
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-> operator, lambda(params, expr) function
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~~~~~~~~~~~~~~
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Allows describing a lambda function for passing to a higher-order function. The left side of the arrow has a formal parameter - 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.
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Examples: ``x -> 2 * x, str -> str != Referer.``
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Higher-order functions can only accept lambda functions as their functional argument.
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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.
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For all functions other than 'arrayMap' and 'arrayFilter', the first argument (the lambda function) can be omitted. In this case, identical mapping is assumed.
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arrayMap(func, arr1, ...)
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~~~~~~~~~~~~
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Returns an array obtained from the original application of the 'func' function to each element in the 'arr' array.
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arrayFilter(func, arr1, ...)
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~~~~~~~~~~~~~
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Returns an array containing only the elements in 'arr1' for which 'func' returns something other than 0.
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Examples:
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.. code-block:: sql
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SELECT arrayFilter(x -> x LIKE '%World%', ['Hello', 'abc World']) AS res
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┌─res───────────┐
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│ ['abc World'] │
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└───────────────┘
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SELECT
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arrayFilter(
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(i, x) -> x LIKE '%World%',
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arrayEnumerate(arr),
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['Hello', 'abc World'] AS arr)
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AS res
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┌─res─┐
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│ [2] │
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└─────┘
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arrayCount([func,] arr1, ...)
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~~~~~~~~~
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Returns the number of elements in 'arr' for which 'func' returns something other than 0. If 'func' is not specified, it returns the number of non-zero items in the array.
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arrayExists([func,] arr1, ...)
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~~~~~~~~~~
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Returns 1 if there is at least one element in 'arr' for which 'func' returns something other than 0. Otherwise, it returns 0.
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arrayAll([func,] arr1, ...)
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~~~~~~~~~
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Returns 1 if 'func' returns something other than 0 for all the elements in 'arr'. Otherwise, it returns 0.
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arraySum([func,] arr1, ...)
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~~~~~~~~~~~
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Returns the sum of the 'func' values. If the function is omitted, it just returns the sum of the array elements.
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arrayFirst(func, arr1, ...)
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~~~~~~~~~
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Returns the first element in the 'arr1' array for which 'func' returns something other than 0.
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arrayFirstIndex(func, arr1, ...)
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~~~~~~~
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Returns the index of the first element in the 'arr1' array for which 'func' returns something other than 0.
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