I am trying to do the simple task of finding if a (string) element exists in an array. The "contains" function works with a one-dimensional array, but not in a 2-dimensional array. Any suggestions? (Documentation on this function appears to be sparse, or I don't know where to look.)
5 Answers
The Swift standard library does not have "multi-dimensional arrays",
but if you refer to "nested arrays" (i.e. an array of arrays) then
a nested contains() would work, for example:
let array = [["a", "b"], ["c", "d"], ["e", "f"]]
let c = array.contains { $0.contains("d") }
print(c) // true
Here the inner contains() method is
public func contains(element: Self.Generator.Element) -> Bool
and the outer contains() method is the predicate-based
public func contains(@noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Bool
which returns true as soon as the given element is found in one
of the inner arrays.
This approach can be generalized to deeper nesting levels.
1 Comment
geoffry
Thanks! The Swift documentation does refer to multidimensional arrays but doesn't give much information on using them.
Updated for Swift 3
The flatten method has been renamed to joined now. So the usage would be
[[1, 2], [3, 4], [5, 6]].joined().contains(3) // true
For multi-dimensional array, you can use flatten to decrease one dimension. So for two-dimensional array:
[[1, 2], [3, 4], [5, 6]].flatten().contains(7) // false
[[1, 2], [3, 4], [5, 6]].flatten().contains(3) // true
Comments
Not as good as J.Wangs answer but another alternative - You can reduce the list to a single boolean value using the reduce(,combine:) function.
[[1,2], [3,4], [5,6]].reduce(false, combine: {$0 || $1.contains(4)})
Comments
You can also write an extension (Swift 3):
extension Sequence where Iterator.Element: Sequence {
func contains2D(where predicate: (Self.Iterator.Element.Iterator.Element) throws -> Bool) rethrows -> Bool {
return try contains(where: {
try $0.contains(where: predicate)
})
}
}
Comments
let array = [["a", "b"], ["c", "d"], ["e", "f"]]
var c = array.contains { $0.contains("d") }
print(c) // true
c = array.contains{$0[1] == "d"}
print(c) // true
c = array.contains{$0[0] == "c"}
print (c) // true
if let indexOfC = array.firstIndex(where: {$0[1] == "d"}) {
print(array[indexOfC][0]) // c
print(array[indexOfC][1]) // d
} else {
print ("Sorry, letter is not in position [][letter]")
}
if let indexOfC = array.firstIndex(where: {$0[0] == "c"}) {
print(array[indexOfC][1]) // d
print(array[indexOfC][0]) // c
} else {
print ("Sorry, letter is not in position [letter][]")
}
1 Comment
Tyler2P
Please don't post only code as answer, but also provide an explanation what your code does and how it solves the problem of the question. Answers with an explanation are usually more helpful and of better quality, and are more likely to attract upvotes.