Java Reference
In-Depth Information
"the", "lazy",
↵
"dog"]
Now we can use the
reduce()
function to calculage the total number of letters in the
sentence:
total = words.reduce( function(prev,word) {
return prev + word.length;
},0);
<< 36
average = total/words.length;
<< 4
Using map() and
reduce()
Together
The
map()
and
reduce()
methods are often used in combination to create some power-
ful transformations of data stored in arrays. Because the
map()
function returns the trans-
formed array, the
reduce()
can be chained on the end. For example, we can calculate the
sum of square numbers using the
map()
method to square each number in the array and
then use the
reduce()
method to add the results together:
[1,2,3].map(square).reduce( function(total,x) { return x +
total; });
<< 14
Another more complex example could be used to take an array of orders, apply a sales tax
to them using
map()
and then use
reduce()
to find the total:
var sales = [ 100, 230, 55];
totalAfterTaxSales = sales.map( function(amount) {
return amount * 1.15; // add 15% sales tax
}).reduce( function(prev,current){
return prev + current;
});
<< 442.75
