Reordering arrays

Question

Say  I have an array that looks like this   var playlist          artist  Herbie Hancock   title  Thrust         artist  Lalo Schifrin   title  Shifting Gears         artist  Faze-O   title  Riding High        How can I move an element to another position   I want to move for example   artist  Lalo Schifrin   title  Shifting Gears   to the end   I tried using splice  like this   var tmp   playlist splice 2 1   playlist splice 2 0 tmp     But it doesn t work

User · Answer

As a simple mutable solution you can call splice twice in a row:

playlist.splice(playlist.length - 1, 1, ...playlist.splice(INDEX_TO_MOVE, 1))

On the other hand, a simple inmutable solution could use slice since this method returns a copy of a section from the original array without changing it:

const copy = [...playlist.slice(0, INDEX_TO_MOVE - 1), ...playlist.slice(INDEX_TO_MOVE), ...playlist.slice(INDEX_TO_MOVE - 1, INDEX_TO_MOVE)]

User · Answer

Here is an immutable version for those who are interested   function immutableMove arr  from  to      return arr reduce  prev  current  idx  self    gt        if  from     to          prev push current             if  idx     from          return prev            if  from  lt  to          prev push current             if  idx     to          prev push self from              if  from  gt  to          prev push current             return prev

User · Answer

Try this    playlist   playlist concat playlist splice 1  1

User · Answer

EDIT  Please check out Andy s answer as his answer came first and this is solely an extension of his I know this is an old question  but I think it s worth it to include Array prototype sort    Here s an example from MDN along with the link var numbers    4  2  5  1  3   numbers sort function a  b      return a - b      console log numbers        1  2  3  4  5   Luckily it doesn t only work with numbers   arr sort  compareFunction   compareFunction Specifies a function that defines the sort order  If omitted  the array is sorted according to each character s Unicode code point value  according to the string conversion of each element   I noticed that you re ordering them by first name  let playlist          artist  quot Herbie Hancock quot   title  quot Thrust quot         artist  quot Lalo Schifrin quot   title  quot Shifting Gears quot         artist  quot Faze-O quot   title  quot Riding High quot          sort by name playlist sort  a  b    gt      if a artist  lt  b artist    return -1      if a artist  gt  b artist    return  1          else names must be equal   return 0       note that if you wanted to order them by last name you would have to either have a key for both first name  amp  last name or do some regex magic  which I can t do XD Hope that helps

User · Answer

If you know the indexes you could easily swap the elements  with a simple function like this   function swapElement array  indexA  indexB      var tmp   array indexA     array indexA    array indexB     array indexB    tmp     swapElement playlist  1  2         artist   Herbie Hancock   title   Thrust          artist   Faze-O   title   Riding High          artist   Lalo Schifrin   title   Shifting Gears      Array indexes are just properties of the array object  so you can swap its values

User · Answer

Reorder its work This Way   var tmpOrder   playlist oldIndex       playlist splice oldIndex  1       playlist splice newIndex  0  tmpOrder     I hope this will work

User · Answer

You could always use the sort method  if you don t know where the record is at present   playlist sort function  a  b        return a artist     Lalo Schifrin                    1       Move it down the list                  0       Keep it the same

User · Answer

If you only ever want to move one item from an arbitrary position to the end of the array  this should work   function toEnd list  position        list push list splice position  1        return list      If you want to move multiple items from some arbitrary position to the end  you can do   function toEnd list  from  count        list push apply list  list splice from  count        return list      If you want to move multiple items from some arbitrary position to some arbitrary position  try   function move list  from  count  to        var args    from  gt  to   to   to - count  0       args push apply args  list splice from  count        list splice apply list  args        return list

User · Answer

Change 2 to 1 as the first parameter in the splice call when removing the element   var tmp   playlist splice 1  1   playlist splice 2  0  tmp 0

User · Answer

Immutable version  no side effects  doesn   t mutate original array   const testArr    1  2  3  4  5    function move from  to  arr        const newArr       arr        const item   newArr splice from  1  0       newArr splice to  0  item        return newArr     console log move 3  1  testArr         1  4  2  3  5   codepen  https   codepen io mliq pen KKNyJZr

User · Answer

With ES6 you can do something like this   const swapPositions    array  a  b    gt       array a   array b      array b   array a      let array    1 2 3 4 5   swapPositions array 0 1          gt   2  1  3  4  5

User · Answer

The syntax of Array splice is   yourArray splice index  howmany  element1             elementX     Where    index is the position in the array you want to start removing elements from howmany is how many elements you want to remove from index element1       elementX are elements you want inserted from position index    This means that splice   can be used to remove elements  add elements  or replace elements in an array  depending on the arguments you pass   Note that it returns an array of the removed elements   Something nice and generic would be   Array prototype move   function  from  to      this splice to  0  this splice from  1  0         Then just use   var ar    1 2 3 4 5   ar move 0 3   alert ar     2 3 4 1 5   Diagram

[javascript] Reordering arrays

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