Array:
- Array stores duplicate values but same type of elements.
- For example:
- marks = [56, 78, 56, 78, 90];
Set:
- Set doesn’t allow duplicate values.
- For example:
- emp_ids = [101, 102, 103, 104]
Map:
- Map stores Values with Keys.
- Keys must be unique where as values can be duplicated.
- For example:
- accounts = [ [101 : ‘amar’], [102 : ‘annie’], [103 : ‘amar’] ];
Set object methods:
| new Set() | Creates a new set |
| add() | Adds element to set |
| delete() | removes specified element from set |
| hash() | returns true if the value exists |
| clear() | remove all elements |
| forEach() | invokes each element |
| values() | returns an iterator with all values |
| keys() | same as values() |
| entries() | returns [key, value] pairs in Map but [value, value] pairs in Set |
Create new set and add elements:
<!doctype html>
<html>
<body>
<script>
var colors = new Set();
colors.add("black");
colors.add("blue");
colors.add("green");
colors.add("cyan");
colors.add("red");
document.write(colors);
</script>
</body>
</html>
Output : [Object Set]
We can display values of any collection using for-each loop:
<html>
<body>
<script>
var colors = new Set();
colors.add("black");
colors.add("blue");
colors.add("green");
colors.add("cyan");
document.write("Colors are : <br/>");
for(var col of colors){
document.write(col + "<br/>");
}
</script>
</body>
</html>
Construct Set from the Array directly:
<html>
<body>
<script>
var arr = ["black", "blue", "green", "cyan", "red"];
var colors = new Set(arr);
document.write("Colors are : <br/>");
for(var col of colors){
document.write(col + "<br/>");
}
</script>
</body>
</html>
Note: If we create Set from Array – all duplicates will be removed automatically.
<html>
<body>
<script>
var arr = ["a", "e", "i", "o", "u", "i", "e", "u", "a", "i"];
var vowels = new Set(arr);
document.write("Vowels are : <br/>");
for(var v of vowels){
document.write(v + "<br/>");
}
</script>
</body>
</html>
Collect value from set and pass to the function to perform any operation in function:
<html>
<body>
<script>
var nums = new Set([7, 4, 2, 9, 3, 6, 1, 8]);
for(var n of nums){
even(n);
}
function even(x){
if(x%2==0)
document.write(x + "<br/>");
}
</script>
</body>
</html>
forEach() method: invokes function for each set element
<html>
<body>
<script>
var nums = new Set([7, 4, 2, 9, 3, 6, 1, 8]);
nums.forEach(function(n){
if(n%2==0){
document.write(n);
}
})
</script>
</body>
</html>
forEach() with lambda expression:
<!doctype html>
<html>
<body>
<script>
var nums = new Set([7, 4, 2, 9, 3, 6, 1, 8]);
nums.forEach(n => {document.write(n);})
</script>
</body>
</html>
Sum of elements in Set using forEach() method and lambda expression:
<!doctype html>
<html>
<body>
<script>
var nums = new Set([7, 4, 2, 9, 3, 6, 1, 8]);
var sum=0;
nums.forEach(n => sum+=n)
document.write("Sum : " + sum);
</script>
</body>
</html>
values(): this method returns an iterator with set elements:
<!doctype html>
<html>
<body>
<script>
var nums = new Set([7, 4, 2, 9, 3, 6, 1, 8]);
var itr = nums.values();
document.write(itr);
</script>
</body>
</html>
Iterate elements using for/of loop:
<!doctype html>
<html>
<body>
<script>
var nums = new Set([7, 4, 2, 9, 3, 6, 1, 8]);
var itr = nums.values();
for(var x of itr)
{
document.write(x);
}
</script>
</body>
</html>
Iterate elements using next() method:
<!doctype html>
<html>
<body>
<script>
var nums = new Set([7, 4, 2, 9, 3, 6, 1, 8]);
var itr = nums.values();
var x = itr.next();
while(!x.done)
{
document.write(x.value);
x = itr.next();
}
</script>
</body>
</html>