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Elementary List Operations
Creating and Accessing Lists
Creating an integer sequence: <int1>..<int2>
Description: The expression <int1>..<int2> creates a list of consecutive integers starting with <int1> and ending with <int2> . If <int1> is larger than <int2> , then the empty list is returned.
Code  Result
 4..9  [4, 5, 6, 7, 8, 9]
 2..2  [2, 1, 0, 1, 2]
 4..1  []

The length of a list: length(<list>)
Description: This operator returns an integer that is equal to the number of elements in the <list> .
Code  Result
 length([2 ,5 ,7 ,3])  4
 length([2 ,[5, 4, 5] ,7 ,3]_2)  3
 length(1..1000)  1000

Combining the length and the repeat operator allows one to list all elements of a list easily.
repeat(length(list),
println(list_#);
)
One word of caution here: CindyScript is designed in such a way that it is seldom useful to traverse all the elements of a list using the repeat operator. There are more elegant ways.
Testing for containment: contains(<list>,<expr>)
Description: This operator returns either true or false depending on whether <list> contains the element <expr>.
Code  Result
 contains([1,3,4,5],4)  true
 contains([1,3,4,5],7)  false
 contains([1,3,4,5],2*2)  true

List Manipulation
Concatenation of lists: concat(<list1>,<list2>)
Description: This operator creates a list by concatenation of two other lists. This operator can equivalently be written as <list1>++<list2> .
Code  Result
 concat(["a", "b"], ["c", "d"])  ["a", "b", "c", "d"]

Removing elements from lists: remove(<list1>,<list2>)
Description: This operator creates a list by removing all elements that occur in <list2> from <list1> . This operator can equivalently be written as <list1>  <list2> .
Code  Result
 remove([1,3,4,5,1,5,6], [1,3,7])  [4,5,5,6]
 [1,3,4,5,1,5,6][1,3,7]  [4,5,5,6]

Intersection of lists: common(<list1>,<list2>)
Description: This operator creates a list collecting all elements that are in both <list1> and <list1> . In the returned list the elements are sorted and each element occurs at most once. This operator can equivalently be written as <list1>~~<list2> .
Code  Result
 common([1,3,4,5,1,5,6], [1,3,7])  [1,3]
 [1,3,4,5,1,5,6]~~[1,3,7]  [1,3]

Appending an element: append(<list>,<expr>)
Description: This operator returns a list that is created by appending <expr> to the list <list> as its last element.
This operator can equivalently be written as <list>:><expr> .
Code  Result
 append(["a", "b", "c"], "d")  ["a", "b", "c","d"]
 ["a", "b", "c"]:>"d"  ["a", "b", "c","d"]

Prepending an element: prepend(<expr>,<list>)
Description: This operator returns a list that is created by prepending <expr> to the list <list> as its first element.
This operator can equivalently be written as <expr><:<list> .
Code  Result
 prepend("d",["a", "b", "c"])  ["d","a", "b", "c"]
 "d"<:["a", "b", "c"]  ["d","a", "b", "c"]

Traversing Lists
The forall loop: forall(<list>,<expr>)
Description: This operator is useful for applying an operation to all elements of a list. It takes a <list> as first argument. It produces a loop in which <expr> is evaluated for each entry of the list. For each run, the run variable # takes the value of the corresponding list entry.
Example:
a=["this","is","a","list"];
forall(a,println(#))
This code fragment produces the output
The forall loop: forall(<list>,<var>,<expr>)
Description: Similar to forall(<list>,<expr>) , but the run variable is now named <var> .
Applying an expression: apply(<list>,<expr>)
Description: This operator generates a new list by applying the operation <expr> to all elements of a list and collecting the results. As usual, # is the run variable, which successively takes the value of each element in the list.
Code  Result
 apply([1, 2, 3, 4, 5],#^2)  [1, 4, 9, 16, 25]
 apply([1, 2, 3, 4, 5],#+5)  [6, 7, 8, 9, 10]
 apply(1..5, [#,#^2])  [[1, 1], [2, 4], [3, 9], [4, 16], [5, 25]]

Applying an expression: apply(<list>,<var>,<expr>)
Description: Similar to apply(<list>,<expr>) , but the run variable is now named <var> .
Selecting elements of a list: select(<list>,<boolexpr>)
Description: This operator selects all elements of a list for which a certain condition is satisfied. The condition is supposed to be encoded by <boolexpr> . This expression is assumed to return a <bool> value. As usual, # is the run variable, which successively take the value of all elements in the list.
Code  Result
 select(1..10, isodd(#))  [1, 3, 5, 7, 9]
 select(0..10, #+# == #^2)  [0,2]

A highlevel application of the select operator is given by the following example:
divisors(x):=select(1..x,mod(x,#)==0);
primes(n):=select(1..n,length(divisors(#))==2);
println(primes(100))
It produces the output
[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97]
In this example, first a function divisors(x) is defined by selecting those numbers that divide x without any remainder. Then a function primes(n) is defined that selects all numbers between 1 and n that have exactly two divisors. These numbers are the primes.
Selecting elements of a list: select(<list>,<var>,<boolexpr>)
Description: Similar to select(<list>,<boolexpr>) , but the run variable is now named <var>.
Contributors to this page: von Gagern
,
Kortenkamp
and
Richter
.
Page last modified on Thursday 26 of March, 2015 [21:13:36 UTC] by von Gagern.
The content on this page is licensed under the terms of the License.

