Asked  7 Months ago    Answers:  5   Viewed   42 times

I have an array like

vendors = [{
    Name: 'Magenic',
    ID: 'ABC'
  },
  {
    Name: 'Microsoft',
    ID: 'DEF'
  } // and so on... 
];

How do I check this array to see if "Magenic" exists? I don't want to loop, unless I have to. I'm working with potentially a couple thousand records.

 Answers

64

2018 edit: This answer is from 2011, before browsers had widely supported array filtering methods and arrow functions. Have a look at CAFxX's answer.

There is no "magic" way to check for something in an array without a loop. Even if you use some function, the function itself will use a loop. What you can do is break out of the loop as soon as you find what you're looking for to minimize computational time.

var found = false;
for(var i = 0; i < vendors.length; i++) {
    if (vendors[i].Name == 'Magenic') {
        found = true;
        break;
    }
}
Tuesday, June 1, 2021
 
peixotorms
answered 7 Months ago
72
a = [5, 1, 6, 14, 2, 8]
b = [2, 6, 15]

a - b
# => [5, 1, 14, 8]

b - a
# => [15]

(b - a).empty?
# => false
Wednesday, June 9, 2021
 
daiscog
answered 6 Months ago
85

Usage: isEqArrays(arr1, arr2)

//
// Array comparsion
//

function inArray(array, el) {
  for ( var i = array.length; i--; ) {
    if ( array[i] === el ) return true;
  }
  return false;
}

function isEqArrays(arr1, arr2) {
  if ( arr1.length !== arr2.length ) {
    return false;
  }
  for ( var i = arr1.length; i--; ) {
    if ( !inArray( arr2, arr1[i] ) ) {
      return false;
    }
  }
  return true;
}
Thursday, July 29, 2021
 
maniclorn
answered 5 Months ago
74

There is Array.filter():

var numbers = [1, 2, 3, 4, 5];
var filtered = numbers.filter(function(x) { return x > 3; });

// As a JavaScript 1.8 expression closure
filtered = numbers.filter(function(x) x > 3);

Note that Array.filter() is not standard ECMAScript, and it does not appear in ECMAScript specs older than ES5 (thanks Yi Jiang and jAndy). As such, it may not be supported by other ECMAScript dialects like JScript (on MSIE).

Nov 2020 Update: Array.filter is now supported across all major browsers.

Saturday, September 4, 2021
 
Amumu
answered 3 Months ago
93

If you want to comply with the C Standard then your options are:

  • Perform individual == or != tests against each pointer in the target range
    • You could use a hash table or search tree or something to speed this up, if it is a very large set
  • Redesign your code to not require this check.

A "probably works" method would be to cast all of the values to uintptr_t and then do relational comparison. If the system has a memory model with absolute ordering then it should define uintptr_t and preserve that ordering; and if it doesn't have such a model then the relational compare idea never would have worked anyway.

Wednesday, December 1, 2021
 
Antonio
answered 6 Days ago
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