permuting a vector in JS

[Mark Tarver]

This JS program is supposed to give a random permutation of a vector.  

function random_n (n) {

  var r = Math.round(n * Math.random()); 

  return r;}

function remove_nth (n, vector) {

  var before = vector.slice(0,n);

  var after = vector.slice(n+1,vector.length);

  var result = before.concat(after);

  return result;}  

 

function rperm (vector) {

  if (vector.length == 0)

     {return []}

     else

     {var n = random_n(vector.length);

      var x = vector[n];

      var newvector = remove_nth(n, vector);

      var recurse = rperm(newvector);

      var result = recurse.push(x);

      return  result} }  

var numbers = [1,2,3];

var perm = rperm(numbers);

console.log(perm);

It fails on https://repl.it/ with TypeError: recurse.push is not a function

Solutions welcome.

Mark

[Bruno Deferrari]

Don't use an intermediary `result` variable, just return `recurse`
after doing the `push()` call.

The reason is that `push` mutates the array instead of returning a new
one -- what it returns is the new length, so in your code snippet
`result` ends being a number (and numbers don't have a `push` method,
thats why you get that error message).

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--
BD

[Bruno Deferrari]

The documentation for Array's push method is here:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push

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BD