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function map() { | |
emit(1, { | |
sum: this.value, // the field you want stats for | |
min: this.value, | |
max: this.value, | |
count: 1, | |
diff: 0 | |
}); | |
} | |
function reduce(key, values) { | |
return values.reduce(function reduce(previous, current, index, array) { | |
var delta = previous.sum/previous.count - current.sum/current.count; | |
var weight = (previous.count * current.count)/(previous.count + current.count); | |
return { | |
sum: previous.sum + current.sum, | |
min: Math.min(previous.min, current.min), | |
max: Math.max(previous.max, current.max), | |
count: previous.count + current.count, | |
diff: previous.diff + current.diff + delta*delta*weight | |
}; | |
}) | |
} | |
function finalize(key, value) { | |
value.average = value.sum / value.count; | |
value.population_variance = value.diff / value.count; | |
value.population_standard_deviation = Math.sqrt(value.population_variance); | |
value.sample_variance = value.diff / (value.count - 1); | |
value.sample_standard_deviation = Math.sqrt(value.sample_variance); | |
delete value.diff; | |
return value; | |
} |
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