How to count certain elements in array?
Very simple:
var count = 0;
for(var i = 0; i < array.length; ++i){
if(array[i] == 2)
count++;
}
Counting the occurrences / frequency of array elements
const arr = [2, 2, 5, 2, 2, 2, 4, 5, 5, 9];
function foo (array) {
let a = [],
b = [],
arr = [...array], // clone array so we don't change the original when using .sort()
prev;
arr.sort();
for (let element of arr) {
if (element !== prev) {
a.push(element);
b.push(1);
}
else ++b[b.length - 1];
prev = element;
}
return [a, b];
}
const result = foo(arr);
console.log('[' + result[0] + ']','[' + result[1] + ']')
console.log(arr)
PHP - count specific array values
$array = array("Kyle","Ben","Sue","Phil","Ben","Mary","Sue","Ben");
$counts = array_count_values($array);
echo $counts['Ben'];
How do I count the occurrences of a list item?
If you only want a single item's count, use the count
method:
>>> [1, 2, 3, 4, 1, 4, 1].count(1)
3
Important: this is very slow if you are counting multiple different items
Each count
call goes over the entire list of n
elements. Calling count
in a loop n
times means n * n
total checks, which can be catastrophic for performance.
If you want to count multiple items, use Counter
, which only does n
total checks.
How do I count the occurrence of a certain item in an ndarray?
Using numpy.unique
:
import numpy
a = numpy.array([0, 3, 0, 1, 0, 1, 2, 1, 0, 0, 0, 0, 1, 3, 4])
unique, counts = numpy.unique(a, return_counts=True)
>>> dict(zip(unique, counts))
{0: 7, 1: 4, 2: 1, 3: 2, 4: 1}
Non-numpy method using collections.Counter
;
import collections, numpy
a = numpy.array([0, 3, 0, 1, 0, 1, 2, 1, 0, 0, 0, 0, 1, 3, 4])
counter = collections.Counter(a)
>>> counter
Counter({0: 7, 1: 4, 3: 2, 2: 1, 4: 1})
Counting array elements in Python
The method len() returns the number of elements in the list.
Syntax:
len(myArray)
Eg:
myArray = [1, 2, 3]
len(myArray)
Output:
3
Count the number of elements of an array in javascript
You can count the actual number of keys using Object.keys(array).length
:
const answers = [];
answers[71] = { field: 'value'};
answers[31] = { field: 'value'};
console.log(Object.keys(answers).length); // prints 2
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