How to do a factorial?

[robin.speekenbrink]

I currently have a structure sort of like the following:

[
  {
    "factor": 1
  },
  {
    "factor": 2
  },
  {
    "factor": 2
  },
  {
    "factor": 4
  }
]

Where i’d like the total factorial: 1 * 2 * 2 * 4 = 16 added to all objects in the array:

[
  {
    "factor": 1,
    "_totalFactor": 16
  },
  {
    "factor": 2,
    "_totalFactor": 16
  },
  {
    "factor": 2,
    "_totalFactor": 16
  },
  {
    "factor": 4,
    "_totalFactor": 16
  }
]

As the array is of undefined length, i need to be able to ‘walk’ the array and multiply by the previous factor… ?

[catalin]

Hello @robin.speekenbrink ,
The first example that could think of is this.
Technically, you need to multiply them and afterwards to add it to the array.

[robin.speekenbrink]

Awesome, and works like a charm… Its exactly the use of the operator on an array that was hard to find in the docs Great!

[robin.speekenbrink]

Thanks for the help, but i just found out I need something similar yet different:

@robin.speekenbrink

[
  {
    "factor": 1
  },
  {
    "factor": 2
  },
  {
    "factor": 2
  },
  {
    "factor": 4
  }
]

should become:

[
  {
    "factor": 1,
   "_totalFactor": 1
  },
  {
    "factor": 2,
   "_totalFactor": 2
  },
  {
    "factor": 2,
   "_totalFactor": 4
  },
  {
    "factor": 4,
   "_totalFactor": 16
  }
]

( thus the “_totalFactor” per object is the previous _totalFactor * factor )

If adding to the orginal array an object { "factor": 5 } this would result in another object in the result: { "factor": 5, "_totalFactor": 80 } ( 5*16 )

[catalin]

Interesting, well broken down like this, you need to keep the “_totalFactor” last value inside a storage, and get it from there for every new element added to the array.

[robin.speekenbrink]

Hmm… sounds complicated as in PHP this would be a very simple foreach-loop:

foreach ($data as $key => &$_obj) {
    $_obj['_totalFactor'] = ($data[$key-1]['_totalFactor'] ?? 1) * $_obj['factor'];
}
unset($_obj); // to clear the reference

You suggest using a storage (i assume to do the lookup of the previous _totalFactor, but how would that work if this was run simultaneously ? I’d also have to introduce somesort of unique key, cleanup the storage afterwards etc… Seems clunkly

[catalin]

Mostly “everything” can also be done in Alumio.
Indeed it required more set up than a regular equivalent PHP code.
But the purpose is to achieve your scope, and from there you can optimize.
Proposed solution in Alumio.

[robin.speekenbrink]

Once you read it like you have it, it actually seems legit

Awesome!