How to return first 5 objects of Array in Swift

Question

In Swift  is there a clever way of using the higher order methods on Array to return the 5 first objects   The obj-c way of doing it was saving an index  and for-loop through the array incrementing index until it was 5 and returning the new array  Is there a way to do this with filter  map or reduce

User · Answer

SWIFT 4  A different solution   An easy inline solution that wont crash if your array is too short   0 1 2 3 4 5  enumerated   compactMap   0 offset  lt  3    0 element   nil     But works fine with this    0 1 2 3 4 5  enumerated   compactMap   0 offset  lt  1000    0 element   nil     Usually this would crash if you did this     0 1 2 3 4 5  prefix upTo  1000     THIS CRASHES   0 1 2 3 4 5  prefix 1000     THIS DOESNT

User · Answer

With Swift 5  according to your needs  you may choose one of the 6 following Playground codes in order to solve your problem      1  Using subscript     subscript  let array     A    B    C    D    E    F    G    H    I    J    K    L   let arraySlice   array    lt 5    let arraySlice   array 0   lt 5     also works   let arraySlice   array 0   4     also works   let arraySlice   array    4     also works let newArray   Array arraySlice  print newArray     prints    A    B    C    D    E        2  Using prefix     method  Complexity  O 1  if the collection conforms to RandomAccessCollection  otherwise  O k   where k is the number of elements to select from the beginning of the collection   let array     A    B    C    D    E    F    G    H    I    J    K    L   let arraySlice   array prefix 5  let newArray   Array arraySlice  print newArray     prints    A    B    C    D    E     Apple states for prefix          If the maximum length exceeds the number of elements in the collection  the result contains all the elements in the collection       3  Using prefix upTo   method  Complexity  O 1   let array     A    B    C    D    E    F    G    H    I    J    K    L   let arraySlice   array prefix upTo  5  let newArray   Array arraySlice  print newArray     prints    A    B    C    D    E     Apple states for prefix upTo        Using the prefix upTo   method is equivalent to using a partial half-open range as the collection s subscript  The subscript notation is preferred over prefix upTo         4  Using prefix through   method  let array     A    B    C    D    E    F    G    H    I    J    K    L   let arraySlice   array prefix through  4  let newArray   Array arraySlice  print newArray     prints    A    B    C    D    E        5  Using removeSubrange     method  Complexity  O n   where n is the length of the collection   var array     A    B    C    D    E    F    G    H    I    J    K    L   array removeSubrange 5     print array     prints    A    B    C    D    E        6  Using dropLast     method  Complexity  O 1  if the collection conforms to RandomAccessCollection  otherwise  O k   where k is the number of elements to drop   let array     A    B    C    D    E    F    G    H    I    J    K    L   let distance   array distance from  5  to  array endIndex  let arraySlice   array dropLast distance  let newArray   Array arraySlice  print newArray     prints    A    B    C    D    E

User · Answer

By far the neatest way to get the first N elements of a Swift array is using prefix   maxLength  Int    let someArray    1  2  3  4  5  6  7  let first5   someArray prefix 5     1  2  3  4  5   This has the benefit of being bounds safe  If the count you pass to prefix is larger than the array count then it just returns the whole array   NOTE  as pointed out in the comments  Array prefix actually returns an ArraySlice  not an Array  In most cases this shouldn t make a difference but if you need to assign the result to an Array type or pass it to a method that s expecting an Array param you will need to force the result into an Array type  let first5   Array someArray prefix 5

User · Answer

The Prefix function is definitely the most efficient way of solving this problem  but you can also use for-in loops like the following  let array    1 2 3 4 5 6 7 8 9  let maxNum   5 var iterationNumber   0 var firstNumbers    Int    if array count  gt  maxNum    for i in array      iterationNumber    1     if iterationNumber  lt   maxNum        firstNumbers append i              firstNumbers remove at  0    print firstNumbers    else     print  quot There were not   maxNum  items in the array  quot      This solution takes up many lines of code but checks to see if there are enough items in the array to carry out the program  then continues and solves the problem  This solution uses many basic functions including array count  which returns the amount of items in the array  not the position of last item in the array  It also uses array append  which adds things onto the end of the array  Lastly  it uses array remove  which removes the array s item that has a specified position  I have tested it it and it works for at least swift 5

User · Answer

let a   Int     0  0  1  1  2  2  3  3  4  let b   Int    Array a prefix 5      result is  0  0  1  1  2

User · Answer

Plain  amp  Simple  extension Array       func first elementCount  Int  - gt  Array             let min   Swift min elementCount  count            return Array self 0   lt min

User · Answer

I slightly changed Markus  answer to update it for the latest Swift version  as var inside your method declaration is no longer supported   extension Array       func takeElements elementCount  Int  - gt  Array           if  elementCount  gt  count                return Array self 0   lt count                     return Array self 0   lt elementCount

User · Answer

Swift 4 with saving array types  extension Array       func take   elementsCount  Int  - gt   Element            let min   Swift min elementsCount  count          return Array self 0   lt min

User · Answer

Swift 4  To get the first N elements of a Swift array you can use prefix   maxLength  Int    Array largeArray prefix 5

User · Answer

Update for swift 4    0 1 2 3 4 5  enumerated   compactMap   0  lt  10000    1   nil     For swift 3    0 1 2 3 4 5  enumerated   flatMap   0  lt  10000    1   nil

User · Answer

Update  There is now the possibility to use prefix to get the first n elements of an array  Check  mluisbrown s answer for an explanation how to use prefix   Original Answer  You can do it really easy without filter  map or reduce by just returning a range of your array   var wholeArray    1  2  3  4  5  6  var n   5  var firstFive   wholeArray 0   lt n     1 2 3 4 5

User · Answer

For an array of objects you can create an extension from Sequence   extension Sequence       func limit   max  Int  - gt   Element            return self enumerated                filter    0 offset  lt  max                map    0 element             Usage    struct Apple     let apples   Apple     Apple    Apple    Apple    let limitTwoApples   apples limit 2      limitTwoApples   Apple    Apple

User · Answer

For getting the first 5 elements of an array  all you need to do is slice the array in question  In Swift  you do it like this  array 0   lt 5    To make picking the N first elements of an array a bit more functional and generalizable  you could create an extension method for doing it  For instance   extension Array       func takeElements var elementCount  Int  - gt  Array           if  elementCount  gt  count                elementCount   count                   return Array self 0   lt elementCount

[arrays] How to return first 5 objects of Array in Swift?

Examples related to arrays

Examples related to swift