Question

I’ve never tried map/reduce.

How would I get the oldest of each type of animal?

My data is like this:

[
{
  "cateory": "animal",
  "type": "cat",
  "age": 4,
  "id": "a"
},
{
  "cateory": "animal",
  "type": "bird",
  "age": 3,
  "id": "b"
},
{
  "cateory": "animal",
  "type": "cat",
  "age": 7
  "id": "c"
},
{
  "cateory": "animal",
  "type": "bird",
  "age": 4,
  "id": "d"
},
{
  "cateory": "animal",
  "type": "cat",
  "age": 8,
  "id": "e"
},
{
  "cateory": "company",
  "type": "Internet",
  "age": 5,
  "id": "Facebook"
}
]

I’m using node-mongodb-native. Thanks!

Answer 1

Your map function should look something like this:

map = function() {
  emit({type: this.type}, {age: this.age});
}

And the reduce function:

reduce = function(key, values) {
  maxAge = 0;
  values.forEach(function(v) {
    if (maxAge < v['age']) {
       maxAge = v['age'];
    }
  });

  return {age: maxAge};
}