Reducer is just a simple function which takes an array of real numbers and returns a representative number by
reducing the array. A reducer can only be applied on a measure. When groupBy
is applied on a DataModel, it
performs aggregation on all measures with a reducer function. Reducer function for a measure can be set from schema
or it can be overridden when groupBy
is called.
DataModel provides reducers which can be used out of the box
Reducer Name | Description |
---|---|
sum | returns the sum of all the number |
avg | returns the avg of all the number |
min | returns the minimum of all the number |
max | returns the maximum of all the number |
first | returns the first number in an array |
last | returns the last number in an array |
count | returns number of elements in the array |
variance | returns the variance of the numbers from the mean |
std | returns the standard deviation of the numbers |
// An function to calculate mean squared value of an array.
function (arr) {
const squaredVal = arr.map(item => item * item);
let sum = 0;
for (let i = 0, l = squaredVal.length; i < l; i++) {
sum += squaredVal[i];
}
return sum;
}
Parameters:
Name | Type | Description |
arr | Array of Number |
array of numbers which needs to be reduced to a single number. |