Count elements in an array

[Rafal Konopka]

How can you caount the number of occurrences of elements in an array? For
example

var arr1 =
[1,5,1,1,5,2,4,5,2,3,2,4,2,4,2,3,2,3,2,4,2,3,2,4,2,5,1,4,2,4,2,3,2,4,1];

how can I count how many 1s, 2s, 3s, etc.?

Despite the example, I never actually know what elements (and how many) the
array holds, which means, that the following is NOT a solution for me:

for( var i =0; i <arr1.length; i++) {
if (arr1 ==1) cnt1++;
if (arr1 ==2) cnt2++;
etc.
}

Thanks,

Rafal

 

[Janwillem Borleffs]

How can you caount the number of occurrences of elements in an array?
For example

var arr1 =
[1,5,1,1,5,2,4,5,2,3,2,4,2,4,2,3,2,3,2,4,2,3,2,4,2,5,1,4,2,4,2,3,2,4,1];

how can I count how many 1s, 2s, 3s, etc.?

http://www.php.net/manual/en/function.array-count-values.php


JW

 

[Janwillem Borleffs]

http://www.php.net/manual/en/function.array-count-values.php

Sorry, thought I was reading a PHP newsgroup...


JW

 

[Ivo]

How can you caount the number of occurrences of elements in an array? For
example

var arr1 =
[1,5,1,1,5,2,4,5,2,3,2,4,2,4,2,3,2,3,2,4,2,3,2,4,2,5,1,4,2,4,2,3,2,4,1];

how can I count how many 1s, 2s, 3s, etc.?

Despite the example, I never actually know what elements (and how many) the
array holds

Several approaches exist. This one retuns an object with the array values as
keys and the number of times they occur as values:

function countvalues(a) {
var b = {}, i = a.length, j;
while( i-- ) {
j = b[a];
b[a] = j ? j+1 : 1;
}
return b;
}

var arr=['you','you','you','me','me','them','them','others'];
alert( countvalues(arr)['you'] ); // 3

hth

 

[Janwillem Borleffs]

How can you caount the number of occurrences of elements in an array?
For example

var arr1 =
[1,5,1,1,5,2,4,5,2,3,2,4,2,4,2,3,2,3,2,4,2,3,2,4,2,5,1,4,2,4,2,3,2,4,1];

how can I count how many 1s, 2s, 3s, etc.?

The following might be useful:

var arr1 =
[1,5,1,1,5,2,4,5,2,3,2,4,2,4,2,3,2,3,2,4,2,3,2,4,2,5,1,4,2,4,2,3,2,4,1];
var count = [];
var msg = '';

for (var i = 0; i < arr1.length; i++) {
if (count[arr1]) {
count[arr1] += 1;
} else {
count[arr1] = 1;
}
}

for (i in count) msg += i + ' occurres ' + count + ' times\n';
alert(msg);


JW

 

[Rafal Konopka]

Thank,

I'll give it a whirl and see what happens

Rafal

 

[Rafal Konopka]

Ivo, It's a nice and crisp solution, but I cannot pass a parameter to the
function as I never know what elements the array holds.

Essentiall, I was wondering if the newer versions of javascript had
something similar to (and oh-so-useful) Perl's

$count{$val}++;

vivifying the hash by creating the key (the unknown element) and value (its
count).

Rafak

 

[RobB]

Ivo, It's a nice and crisp solution, but I cannot pass a parameter to the
function as I never know what elements the array holds.

Essentiall, I was wondering if the newer versions of javascript had
something similar to (and oh-so-useful) Perl's

$count{$val}++;

vivifying the hash by creating the key (the unknown element) and value (its
count).

Rafak

Several approaches exist. This one retuns an object with the array

values

as
keys and the number of times they occur as values:

function countvalues(a) {
var b = {}, i = a.length, j;
while( i-- ) {
j = b[a];
b[a] = j ? j+1 : 1;
}
return b;
}

var arr=['you','you','you','me','me','them','them','others'];
alert( countvalues(arr)['you'] ); // 3

hth

Maybe...

Array.prototype.countvalues = function(k)
{
var b = {}, i = this.length, j;
while( i-- )
{
j = b[this];
b[this] = j ? j+1 : 1;
}
return b[k];
}

var arr=['you','you','you','me','m­e','them','them','others'];
alert( arr.countvalues('you') ) // 3

This won't distinguish between string/numeric primitives ('4' / 4)
however; don't think you can hash with these as JS objects treat
string/numeric integer subscripts similarly.

 

[RobG]

Ivo, It's a nice and crisp solution, but I cannot pass a parameter to the
function as I never know what elements the array holds.

If you just want to get a reduced array with unique elements and
the count of occurrences, then Ivo's solution actually does
exactly that. You just need to modify the output:

<script type="text/javascript">
function countvalues(a) {
var b = {}, i = a.length, j;
while( i-- ) {
j = b[a];
b[a] = j ? j+1 : 1;
}
return b; // an object of element:count arrays
}

var arr=['you','you','me','you',
'me','them','them',
'others','you'];

var a = countvalues(arr);
var msg='';

// To see how many times each element appears
for (elem in a){
msg += '\n' + elem + ' : ' + a[elem];
}
alert(msg);

// To see how many times a particular element appears
alert( countvalues(arr)['you'] ); // 4

</script>

 

[Rafal Konopka]

Thanks to all who replied to my question (counting elements of an array).
It was in fact very educational.

Rafal