What are the reduceAdd, reduceSum , reduceRemove functions in crossfilter? How should they be used?

Question

Can someone explain in simple terms how reduce function with its arguments reduceAdd, reduceSum, reduceRemove works in crossfilter

Answer 1

http://blog.rusty.io/2012/09/17/crossfilter-tutorial/

var livingThings = crossfilter([
  // Fact data.
  { name: “Rusty”,  type: “human”, legs: 2 },
  { name: “Alex”,   type: “human”, legs: 2 },
  { name: “Lassie”, type: “dog”,   legs: 4 },
  { name: “Spot”,   type: “dog”,   legs: 4 },
  { name: “Polly”,  type: “bird”,  legs: 2 },
  { name: “Fiona”,  type: “plant”, legs: 0 }
]);

For example, how many living things are in my house?

To do this, we’ll call the groupAll convenience function, which selects all records into a single group, and then the reduceCount function, which creates a count of the records.

// How many living things are in my house?
var n = livingThings.groupAll().reduceCount().value();
console.log("There are " + n + " living things in my house.") // 6

Now let’s get a count of all the legs in my house. Again, we’ll use the groupAll function to get all records in a single group, but then we call the reduceSum function. This is going to sum values together. What values? Well, we want legs, so let’s pass a function that extracts and returns the number of legs from the fact.

// How many total legs are in my house?
var legs = livingThings.groupAll().reduceSum(function(fact) {
  return fact.legs;
}).value()
console.log("There are " + legs + " legs in my house.")

reduceCount function creates a count of the records.
reduceSum function is the sum values of these records.