Deterministic First/Last

functions.diff

diff --git a/influxql/functions.go b/influxql/functions.go
index 3d75c5a..918f241 100644
--- a/influxql/functions.go
+++ b/influxql/functions.go
@@ -949,6 +949,8 @@ func MapFirst(itr Iterator) interface{} {
                if k < out.Time {
                        out.Time = k
                        out.Val = v
+               } else if k == out.Time && greaterThan(v, out.Val) {
+                       out.Val = v
                }
        }
        if pointsYielded {
@@ -976,6 +978,8 @@ func ReduceFirst(values []interface{}) interface{} {
                if val.Time < out.Time {
                        out.Time = val.Time
                        out.Val = val.Val
+               } else if val.Time == out.Time && greaterThan(val.Val, out.Val) {
+                       out.Val = val.Val
                }
        }
        if pointsYielded {
@@ -999,6 +1003,8 @@ func MapLast(itr Iterator) interface{} {
                if k > out.Time {
                        out.Time = k
                        out.Val = v
+               } else if k == out.Time && greaterThan(v, out.Val) {
+                       out.Val = v
                }
        }
        if pointsYielded {
@@ -1027,6 +1033,8 @@ func ReduceLast(values []interface{}) interface{} {
                if val.Time > out.Time {
                        out.Time = val.Time
                        out.Val = val.Val
+               } else if val.Time == out.Time && greaterThan(val.Val, out.Val) {
+                       out.Val = val.Val
                }
        }
        if pointsYielded {
@@ -1078,6 +1086,20 @@ func ReducePercentile(percentile float64) ReduceFunc {
        }
 }

+func greaterThan(a, b interface{}) bool {
+       switch t := a.(type) {
+       case int64:
+               return t > b.(int64)
+       case float64:
+               return t > b.(float64)
+       case string:
+               return t > b.(string)
+       case bool:
+               return t == true
+       }
+       return false
+}
+
 // IsNumeric returns whether a given aggregate can only be run on numeric fields.
 func IsNumeric(c *Call) bool {
        switch c.Name {