Finding out how many times an array element appears

by
  • Keep a variable for the total count
  • Loop through the array and check if current value is the same as the one you’re looking for, if it is, increment the total count by one
  • After the loop, total count contains the number of times the number you were looking for is in the array

Show your code and we can help you figure out where it went wrong

Here’s a simple implementation (since you don’t have the code that didn’t work)

var list = [2, 1, 4, 2, 1, 1, 4, 5];  

function countInArray(array, what) {
    var count = 0;
    for (var i = 0; i < array.length; i++) {
        if (array[i] === what) {
            count++;
        }
    }
    return count;
}

countInArray(list, 2); // returns 2
countInArray(list, 1); // returns 3

countInArray could also have been implemented as

function countInArray(array, what) {
    return array.filter(item => item == what).length;
}

More elegant, but maybe not as performant since it has to create a new array.

More Related Contents:

  1. Filter JSON by key value with JavaScript
  2. Accesing 2d arrays from Javascript [closed]
  3. How to remove all duplicates from an array of objects?
  4. Determine whether an array contains a value [duplicate]
  5. Javascript call() & apply() vs bind()?
  6. Best way to find if an item is in a JavaScript array? [duplicate]
  7. How to convert an Object {} to an Array [] of key-value pairs in JavaScript
  8. What is “undefined x 1” in JavaScript?
  9. Why Array.indexOf doesn’t find identical looking objects
  10. How to count the number of occurrences of each item in an array? [duplicate]
  11. JavaScript – why Array.prototype.fill actually fills a “pointer” of object when filling anything like ‘new Object()’
  12. Convert object array to hash map, indexed by an attribute value of the Object
  13. Check if array contains all elements of another array
  14. Unpacking array into separate variables in JavaScript
  15. How to convert array into string without comma and separated by space in javascript without concatenation?
  16. JavaScript arrays braces vs brackets
  17. Using Array objects as key for ES6 Map
  18. Convert object to array of key–value objects like `{ name: “Apple”, value: “0.6” }`
  19. How to find index of an object by key and value in an javascript array
  20. jQuery min/max property from array of elements
  21. remove item from array using its name / value
  22. JavaScript filter array by data from another
  23. How to convert an array into an object in javascript with mapped key-value pairs?
  24. How do I unset an element in an array in javascript?
  25. javascript – match string against the array of regular expressions
  26. How to find the coordinate that is closest to the point of origin?
  27. Compare two Arrays with Objects and create new array with unmatched objects
  28. Difference between ( for… in ) and ( for… of ) statements?
  29. Find object having maximum value for the `id` property in an array of objects
  30. Why do these two javascript 2d-arrays behave differently?

Leave a Comment