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Mongo map reduce functions to calculate sum, min, max, count, average, population variance, sample variance, population standard deviation, sample standard deviation Public Domain License
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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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