112 lines
3.0 KiB
Plaintext
112 lines
3.0 KiB
Plaintext
// We often need our programs to perform operations on
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// collections of data, like selecting all items that
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// satisfy a given predicate or mapping all items to a new
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// collection with a custom function.
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// In some languages it's idiomatic to use [generic](http://en.wikipedia.org/wiki/Generic_programming)
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// data structures and algorithms. Go does not support
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// generics; in Go it's common to provide collection
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// functions if and when they are specifically needed for
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// your program and data types.
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// Here are some example collection functions for slices
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// of `strings`. You can use these examples to build your
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// own functions. Note that in some cases it may be
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// clearest to just inline the collection-manipulating
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// code directly, instead of creating and calling a
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// helper function.
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package main
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import "strings"
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import "fmt"
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// Returns the first index of the target string `t`, or
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// -1 if no match is found.
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func Index(vs []string, t string) int {
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for i, v := range vs {
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if v == t {
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return i
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}
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}
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return -1
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}
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// Returns `true` if the target string t is in the
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// slice.
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func Include(vs []string, t string) bool {
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return Index(vs, t) >= 0
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}
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// Returns `true` if one of the strings in the slice
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// satisfies the predicate `f`.
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func Any(vs []string, f func(string) bool) bool {
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for _, v := range vs {
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if f(v) {
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return true
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}
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}
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return false
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}
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// Returns `true` if all of the strings in the slice
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// satisfy the predicate `f`.
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func All(vs []string, f func(string) bool) bool {
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for _, v := range vs {
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if !f(v) {
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return false
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}
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}
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return true
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}
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// Returns a new slice containing all strings in the
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// slice that satisfy the predicate `f`.
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func Filter(vs []string, f func(string) bool) []string {
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vsf := make([]string, 0)
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for _, v := range vs {
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if f(v) {
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vsf = append(vsf, v)
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}
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}
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return vsf
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}
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// Returns a new slice containing the results of applying
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// the function `f` to each string in the original slice.
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func Map(vs []string, f func(string) string) []string {
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vsm := make([]string, len(vs))
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for i, v := range vs {
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vsm[i] = f(v)
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}
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return vsm
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}
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func main() {
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// Here we try out our various collection functions.
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var strs = []string{"peach", "apple", "pear", "plum"}
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fmt.Println(Index(strs, "pear"))
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fmt.Println(Include(strs, "grape"))
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fmt.Println(Any(strs, func(v string) bool {
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return strings.HasPrefix(v, "p")
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}))
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fmt.Println(All(strs, func(v string) bool {
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return strings.HasPrefix(v, "p")
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}))
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fmt.Println(Filter(strs, func(v string) bool {
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return strings.Contains(v, "e")
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}))
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// The above examples all used anonymous functions,
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// but you can also use named functions of the correct
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// type.
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fmt.Println(Map(strs, strings.ToUpper))
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}
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