How do I get the number of elements in an array with non-consecutive numbers as keys?
var array = [];
array[5] = "something";
array[10] = "nothing":
expected:
number of elements in array = 2
actual:
instead I get the last number used as the "length", 11
I can figure out the way to do this by iterating through each element. Is there is better way to do this?
You may count non empty cells:
array.filter(function(e){return e!==undefined}).length
array.filter(Boolean) would be more concise. Also, could you explain your answer a bit more?
Boolean?0 and "", which may be valid values.Sounds like what you actually want is a dictionary, not an array. Have you considered that as an alternative data structure?
How to do associative array/hashing in JavaScript
var myArray = {};
myArray["5"] = "something";
myArray["10"] = "nothing";
And to get the length you would want to write a quick function like the one shown here:
Object.size = function(obj) {
var size = 0, key;
for (key in obj) {
if (obj.hasOwnProperty(key)) size++;
}
return size;
};
var size = Object.size(myArray);
Or alternatively, even simpler (but not supported by IE8):
Object.keys(myArray).length
Map is closer. Set and Map have low browser support still though.var array = [];
array[5] = "something";
array[10] = "nothing":
Your array in this case becomes :
[undefined,undefined,undefined,undefined,undefined,"something",undefined,undefined,undefined,undefined,"nothing"]
thats why the length is coming as 11. So ideally you should not set it like array[5] or array[10].
If you have variable keys, then you should use object
a = {};
a["5"] = "something";
a["10"] = "nothing"
Then a will look like {"5":"something","10":"nothing"}
Then you can calculate count as :
var elemCount = 0;
for(var key in a){
elemCount++;
}
Output:
elemCount = 2
Various other ways of getting length of keys in object: How to efficiently count the number of keys/properties of an object in JavaScript?
var array= Array(5);
array[1] = 10;
array[3] = 3;
numberOfElements = 0;
for(var i =0; i<array.length; i++) {
if(array[i]!=undefined)
numberOfElements++;
}
alert(numberOfElements);
!== operator in case the user put nulls in the array.
0, if you assign some value at indexn, length of array will beMaximum value of n + 1lengthwill be11, not10