Q 语言 - 内置函数
q编程语言拥有一组丰富而强大的内置函数。 内置函数可以是以下类型 −
字符串函数 − 接受一个字符串作为输入并返回一个字符串。
聚合函数 − 将列表作为输入并返回一个原子。
统计函数 − 获取一个列表并返回相同计数的列表。
数学函数 − 接受数字参数并返回数字参数。
其他功能 − 除上述以外的所有功能。
字符串函数
Like − 模式匹配
q)/like is a dyadic, performs pattern matching, return 1b on success else 0b q)"John" like "J??n" 1b q)"John My Name" like "J*" 1b
ltrim − 删除前导空格
q)/ ltrim - monadic ltrim takes string argument, removes leading blanks q)ltrim " Rick " "Rick "
rtrim − 删除尾随空格
q)/rtrim - takes string argument, returns the result of removing trailing blanks q)rtrim " Rick " " Rick"
ss − 字符串搜索
q)/ss - string search, perform pattern matching, same as "like" but return the indices of the matches of the pattern in source. q)"Life is beautiful" ss "i" 1 5 13
trim − 删除前导和尾随空格
q)/trim - takes string argument, returns the result of removing leading & trailing blanks q)trim " John " "John"
数学函数
acos − 余弦的反函数
q)/acos - inverse of cos, for input between -1 and 1, return float between 0 and pi q)acos 1 0f q)acos -1 3.141593 q)acos 0 1.570796
cor − 给出关联性
q)/cor - the dyadic takes two numeric lists of same count, returns a correlation between the items of the two arguments q)27 18 18 9 0 cor 27 36 45 54 63 -0.9707253
cross − 笛卡尔积
q)/cross - takes atoms or lists as arguments and returns their Cartesian product q)9 18 cross `x`y`z 9 `x 9 `y 9 `z 18 `x 18 `y 18 `z
var − 方差
q)/var - monadic, takes a scaler or numeric list and returns a float equal to the mathematical variance of the items q)var 45 0f q)var 9 18 27 36 101.25
wavg
q)/wavg - dyadic, takes two numeric lists of the same count and returns the average of the second argument weighted by the first argument. q)1 2 3 4 wavg 200 300 400 500 400f
聚合函数
all − & 运算
q)/all - monadic, takes a scaler or list of numeric type and returns the result of & applied across the items. q)all 0b 0b q)all 9 18 27 36 1b q)all 10 20 30 1b
Any − | 运算
q)/any - monadic, takes scaler or list of numeric type and the return the result of | applied across the items q)any 20 30 40 50 1b q)any 20012.02.12 2013.03.11 '20012.02.12
prd − 算术乘积
q)/prd - monadic, takes scaler, list, dictionary or table of numeric type and returns the arithmetic product. q)prd `x`y`z! 10 20 30 6000 q)prd ((1 2; 3 4);(10 20; 30 40)) 10 40 90 160
Sum − 算术总和
q)/sum - monadic, takes a scaler, list,dictionary or table of numeric type and returns the arithmetic sum. q)sum 2 3 4 5 6 20 q)sum (1 2; 4 5) 5 7
统计的函数
Deltas − 与之前的项目差异。
q)/deltas -takes a scalar, list, dictionary or table and returns the difference of each item from its predecessor. q)deltas 2 3 5 7 9 2 1 2 2 2 q)deltas `x`y`z!9 18 27 x | 9 y | 9 z | 9
fills − 填充空值
q)/fills - takes scalar, list, dictionary or table of numeric type and returns a c copy of the source in which non-null items are propagated forward to fill nulls q)fills 1 0N 2 0N 4 1 1 2 2 4 q)fills `a`b`c`d! 10 0N 30 0N a | 10 b | 10 c | 30 d | 30
maxs − 累计最大值
q)/maxs - takes scalar, list, dictionary or table and returns the cumulative maximum of the source items. q)maxs 1 2 4 3 9 13 2 1 2 4 4 9 13 13 q)maxs `a`b`c`d!9 18 0 36 a | 9 b | 18 c | 18 d | 36
其他函数
Count − 返回元素数量
q)/count - returns the number of entities in its argument. q)count 10 30 30 3 q)count (til 9) 9 q)count ([]a:9 18 27;b:1.1 2.2 3.3) 3
Distinct − 返回不同的实体
q)/distinct - monadic, returns the distinct entities in its argument q)distinct 1 2 3 4 2 3 4 5 6 9 1 2 3 4 5 6 9
Except − 第二个参数中不存在元素。
q)/except - takes a simple list (target) as its first argument and returns a list containing the items of target that are not in its second argument q)1 2 3 4 3 1 except 1 2 3 4 3
fill − 用第一个参数填充 null
q)/fill (^) - takes an atom as its first argument and a list(target) as its second argument and return a list obtained by substituting the first argument for every occurrence of null in target q)42^ 9 18 0N 27 0N 36 9 18 42 27 42 36 q)";"^"Life is Beautiful" "Life;is;Beautiful"
