floats: add ParseWithNA

floats/floats.go

@@ -14,6 +14,7 @@ import (
 	"errors"
 	"math"
 	"sort"
+	"strconv"
 
 	"gonum.org/v1/gonum/internal/asm/f64"
 )
@@ -567,6 +568,19 @@ func Norm(s []float64, L float64) float64 {
 	return math.Pow(norm, 1/L)
 }
 
+// ParseWithNA converts the string s to a float64 in v.
+// If s equals missing, w is returned as 0, otherwise 1.
+func ParseWithNA(s, missing string) (v, w float64, err error) {
+	if s == missing {
+		return 0, 0, nil
+	}
+	v, err = strconv.ParseFloat(s, 64)
+	if err == nil {
+		w = 1
+	}
+	return v, w, err
+}
+
 // Prod returns the product of the elements of the slice.
 // Returns 1 if len(s) = 0.
 func Prod(s []float64) float64 {

floats/parse_example_test.go

@@ -0,0 +1,43 @@
+// Copyright ©2017 The gonum Authors. All rights reserved.
+// Use of this code is governed by a BSD-style
+// license that can be found in the LICENSE file
+
+package floats_test
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"strings"
+
+	"gonum.org/v1/gonum/floats"
+	"gonum.org/v1/gonum/stat"
+)
+
+func ExampleParseWithNA() {
+	// Calculate the mean of a list of numbers
+	// ignoring missing values.
+	const data = `6
+missing
+4
+`
+
+	var vals, weights []float64
+	sc := bufio.NewScanner(strings.NewReader(data))
+	for sc.Scan() {
+		v, w, err := floats.ParseWithNA(sc.Text(), "missing")
+		if err != nil {
+			log.Fatal(err)
+		}
+		vals = append(vals, v)
+		weights = append(weights, w)
+	}
+	err := sc.Err()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(stat.Mean(vals, weights))
+
+	// Output:
+	// 5
+}