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make stddev work #2354

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merged 5 commits into from
Apr 29, 2015
Merged

make stddev work #2354

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fad619a
add test for stddev
neonstalwart Apr 20, 2015
94030b2
return the values from stddev mapper function
neonstalwart Apr 20, 2015
23c38fb
get stddev working
neonstalwart Apr 22, 2015
762a770
unmarshal stddev appropriately
neonstalwart Apr 23, 2015
ee01a5f
add test for stddev on 1 point
neonstalwart Apr 29, 2015
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33 changes: 30 additions & 3 deletions cmd/influxd/server_integration_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -581,14 +581,41 @@ func runTestsData(t *testing.T, testName string, nodes Cluster, database, retent
// Aggregations
{
reset: true,
name: "large mean",
name: "stddev with just one point",
write: `{"database" : "%DB%", "retentionPolicy" : "%RP%", "points": [
{"name": "cpu", "timestamp": "2015-04-20T14:27:41Z", "fields": {"value": 45}}
]}`,
query: `SELECT stddev(value) FROM cpu`,
queryDb: "%DB%",
expected: `{"results":[{"series":[{"name":"cpu","columns":["time","stddev"],"values":[["1970-01-01T00:00:00Z",null]]}]}]}`,
},
{
reset: true,
name: "large mean and stddev",
write: `{"database" : "%DB%", "retentionPolicy" : "%RP%", "points": [
{"name": "cpu", "timestamp": "2015-04-20T14:27:40Z", "fields": {"value": ` + string(maxFloat64) + `}},
{"name": "cpu", "timestamp": "2015-04-20T14:27:41Z", "fields": {"value": ` + string(maxFloat64) + `}}
]}`,
query: `SELECT mean(value) FROM cpu`,
query: `SELECT mean(value), stddev(value) FROM cpu`,
queryDb: "%DB%",
expected: `{"results":[{"series":[{"name":"cpu","columns":["time","mean","stddev"],"values":[["1970-01-01T00:00:00Z",` + string(maxFloat64) + `,0]]}]}]}`,
},
{
reset: true,
name: "mean and stddev",
write: `{"database" : "%DB%", "retentionPolicy" : "%RP%", "points": [
{"name": "cpu", "timestamp": "2000-01-01T00:00:00Z", "fields": {"value": 2}},
{"name": "cpu", "timestamp": "2000-01-01T00:00:10Z", "fields": {"value": 4}},
{"name": "cpu", "timestamp": "2000-01-01T00:00:20Z", "fields": {"value": 4}},
{"name": "cpu", "timestamp": "2000-01-01T00:00:30Z", "fields": {"value": 4}},
{"name": "cpu", "timestamp": "2000-01-01T00:00:40Z", "fields": {"value": 5}},
{"name": "cpu", "timestamp": "2000-01-01T00:00:50Z", "fields": {"value": 5}},
{"name": "cpu", "timestamp": "2000-01-01T00:01:00Z", "fields": {"value": 7}},
{"name": "cpu", "timestamp": "2000-01-01T00:01:10Z", "fields": {"value": 9}}
]}`,
query: `SELECT mean(value), stddev(value) FROM cpu WHERE time >= '2000-01-01' AND time < '2000-01-01T00:02:00Z' GROUP BY time(10m)`,
queryDb: "%DB%",
expected: `{"results":[{"series":[{"name":"cpu","columns":["time","mean"],"values":[["1970-01-01T00:00:00Z",` + string(maxFloat64) + `]]}]}]}`,
expected: `{"results":[{"series":[{"name":"cpu","columns":["time","mean","stddev"],"values":[["2000-01-01T00:00:00Z",5,2.138089935299395]]}]}]}`,
},
{
reset: true,
Expand Down
20 changes: 13 additions & 7 deletions influxql/functions.go
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Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,12 @@ func InitializeUnmarshaller(c *Call) (UnmarshalFunc, error) {
err := json.Unmarshal(b, &o)
return &o, err
}, nil
case "stddev":
return func(b []byte) (interface{}, error) {
val := make([]float64, 0)
err := json.Unmarshal(b, &val)
return val, err
}, nil
default:
return func(b []byte) (interface{}, error) {
var val interface{}
Expand Down Expand Up @@ -386,7 +392,7 @@ func MapStddev(itr Iterator) interface{} {
values = append(values, v.(float64))
}

return nil
return values
}

// ReduceStddev computes the stddev of values.
Expand All @@ -405,21 +411,21 @@ func ReduceStddev(values []interface{}) interface{} {
return nil
}

// Get the sum
var sum float64
// Get the mean
var mean float64
var count int
for _, v := range data {
sum += v
count++
mean += (v - mean) / float64(count)
}
// Get the mean
mean := sum / float64(len(data))
// Get the variance
var variance float64
for _, v := range data {
dif := v - mean
sq := math.Pow(dif, 2)
variance += sq
}
variance = variance / float64(len(data)-1)
variance = variance / float64(count-1)
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Should check for count == 1 or this'll be bad

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look at line 410

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it probably wouldn't be a bad idea to add a test for count < 2 though. i can work on that if you want.

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ah, no, that's fine, didn't see it.

stddev := math.Sqrt(variance)

return stddev
Expand Down