New Array from Index Range Swift

Question

How can I do something like this  Take the first n elements from an array   newNumbers   numbers 0  n    Currently getting the following error   error  could not find an overload for  subscript  that accepts the supplied arguments   EDIT   Here is the function that I m working in   func aFunction numbers  Array lt Int gt   position  Int  - gt  Array lt Int gt        var newNumbers   numbers 0   position      return newNumbers

User · Accepted Answer

This works for me   var test    1  2  3  var n   2 var test2   test 0   lt n    Your issue could be with how you re declaring your array to begin with   EDIT   To fix your function  you have to cast your Slice to an array   func aFunction numbers  Array lt Int gt   position  Int  - gt  Array lt Int gt        var newNumbers   Array numbers 0   lt position       return newNumbers       test aFunction  1  2  3   2     returns  1  2

User · Answer

One more variant using extension and argument name range  This extension uses Range and ClosedRange  extension Array        subscript  range r  Range lt Int gt   - gt  Array           return Array self r               subscript  range r  ClosedRange lt Int gt   - gt  Array           return Array self r             Tests   func testArraySubscriptRange           given     let arr     1    2    3          when     let result   arr range  1   lt arr count  as Array        then     XCTAssertEqual   2    3    result     func testArraySubscriptClosedRange           given     let arr     1    2    3          when     let result   arr range  1   arr count - 1  as Array        then     XCTAssertEqual   2    3    result

User · Answer

subscript extension Array where Element   Equatable     public subscript safe bounds  Range lt Int gt   - gt  ArraySlice lt Element gt        if bounds lowerBound  gt  count   return          let lower   Swift max 0  bounds lowerBound      let upper   Swift max 0  Swift min count  bounds upperBound       return self lower   lt upper           public subscript safe lower  Int     upper  Int   - gt  ArraySlice lt Element gt        let lower   lower    0     let upper   upper    count     if lower  gt  upper   return          return self safe  lower   lt upper         returns a copy of this range clamped to the given limiting range  var arr    1  2  3       arr safe  0   lt 1        returns  1   assert arr safe  0   lt 1      1   arr safe  2   lt 100      returns  3   assert arr safe  2   lt 100      3   arr safe  -100   lt 0     returns      assert arr safe  -100   lt 0          arr safe  0  1         returns  1   assert arr safe  0  1      1   arr safe  2  100       returns  3   assert arr safe  2  100      3   arr safe  -100  0      returns      assert arr safe  -100  0

User · Answer

1  Using Array subscript with range  With Swift 5  when you write      let newNumbers   numbers 0   position        newNumbers is not of type Array lt Int gt  but is of type ArraySlice lt Int gt   That s because Array s subscript      returns an ArraySlice lt Element gt  that  according to Apple  presents a view onto the storage of some larger array   Besides  Swift also provides Array an initializer called init      that allows us to create a new array from a sequence  including ArraySlice    Therefore  you can use subscript      with init      in order to get a new array from the first n elements of an array   let array   Array 10   14      10  11  12  13  14  let arraySlice   array 0   lt 3     using Range   let arraySlice   array 0   2     using ClosedRange also works   let arraySlice   array    lt 3     using PartialRangeUpTo also works   let arraySlice   array    2     using PartialRangeThrough also works let newArray   Array arraySlice  print newArray     prints  10  11  12       2  Using Array s prefix     method  Swift provides a prefix     method for types that conform to Collection protocol  including Array   prefix     has the following declaration   func prefix   maxLength  Int  - gt  ArraySlice lt Element gt       Returns a subsequence  up to maxLength in length  containing the initial elements     Apple also states      If the maximum length exceeds the number of elements in the collection  the result contains all the elements in the collection    Therefore  as an alternative to the previous example  you can use the following code in order to create a new array from the first elements of another array   let array   Array 10   14      10  11  12  13  14  let arraySlice   array prefix 3  let newArray   Array arraySlice  print newArray     prints  10  11  12

User · Answer

Array functional way     array enumerated   filter    0 offset  lt  limit   map    0 element    ranged   array enumerated   filter    0 offset  gt   minLimit  amp  amp   0 offset  lt  maxLimit   map    0 element    The advantage of this method is such implementation is safe

[arrays] New Array from Index Range Swift

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