understanding Underscore.js's _.map() and _.reduce()

gistfile1.js

// this...
var doubles = [];
_.each([1,2,3], function(val){
  doubles.push(val * 2);
});
// ...and this...
var doubles = _.map([1,2,3], function(val){
  return val * 2;
});
// ...are equivalent


// so is this...
var numMales = 0;
_.each(people, function(person){
  if (person.gender === 'M') {
    numMales++;
  }
});
// ...and this
var numMales = _.reduce(people, function(sum, person){
  if (person.gender === 'M') {
    return sum + 1;
  } else {
    return sum;
  }
}, 0);