Golang iterate over array

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Golang iterate over array

This is the chapter 11 of the golang comprehensive tutorial series. Refer to this link for other chapters of the series ? Golang Comprehensive Tutorial Series Next Tutorial ? If ElsePrevious Tutorial ? For Loop Now let's check out the current tutorial. Below is the table of contents for current tutorial. Overview When it comes to loop, golang has: We saw for loop in the last tutorial. In this tutorial, we will be learning about the for-range loop only. for-range loop is used to iterate over different collection data structures in golang such as array or slicestringmapschannel Let's see some examples now Examples Here is the format of for-range when used with array/slice for index, value := range array/slice { //Do something with index and value } This is how for-range loop works in case of array/slice. It iterates over the given array/slice starting from index zero and the body of the for range loop is executed for every value present at the index. Both index and value are optional in for-range when using with array/slice. The below example shows how to use a for-range loop for a slice With index and valueWith value onlyWith index onlyWithout index and value package main import "fmt" func main() { letters := []string{"a", "b", "c"} //With index and value fmt.Println("Both Index and Value") for i, letter := range letters { fmt.Printf("Index: %d Value:%s", i, letter) } //Only value fmt.Println("Only value") for _, letter := range letters { fmt.Printf("Value: %s", letter) } //Only index fmt.Println("Only Index") for i := range letters { fmt.Printf("Index: %d", i) } //Without index and value. Just print array values fmt.Println("Without Index and Value") i := 0 for range letters { fmt.Printf("Index: %d Value: %s", i, letters[i]) i++ } } Output: Both Index and Value Index: 0 Value:a Index: 1 Value:b Index: 2 Value:c Only value Value: a Value: b Value: c Only Index Index: 0 Index: 1 Index: 2 Without Index and Value Index: 0 Value: a Index: 1 Value: b Index: 2 Value: c for-range loop with a string In Golang string is a sequence of bytes. A string literal actually represents a UTF-8 sequence of bytes. In UTF-8, ASCII characters are single-byte corresponding to the first 128 Unicode characters. All other characters are between 1 -4 bytes. To understand it more consider the below string sample := "a?c" In above string `a' takes one byte as per UTF-8`?' takes two bytes as per UTF-8`b' takes one byte as per UTF-8 The above string has 1+2+1 = 4 bytes altogether. Therefore when we try to print the length of the string using the standard len() function it will output 4 and not 3 as len() function returns the number of bytes in the string. fmt.Printf("Length is %d", len(sample)) Hence standalone for loop cannot be used to iterate over all characters of a string as it will iterate over bytes and not character. So below for loop will instead iterate four times and the print value corresponding to the byte present at that index. for i := 0; i < len(sample); i++ { fmt.Printf("%c", sample[i]) } It will output below string which is not same as "a?c" string a?b The above output is not what we want. This is where for-range loop comes into picture for a string. It iterates over the Unicode points( also referred to as rune in golang) in a string and will correctly output a, ?, b. Here is the format when using for-range with string for index, character := range string { //Do something with index and character } Some point to note before we move to a code example index is the starting point of the Unicode character in the string. For example in string "a?c" character "a" starts at index 0 , character "?" starts at index 1 while character "b" starts at index 3.value is the Unicode point or basically each character in the string instead of bytes. It is also called rune. A rune in golang represents a Unicode Code PointBoth index and value are optional Now let's see a code example package main import "fmt" func main() { sample := "a?b" //With index and value fmt.Println("Both Index and Value") for i, letter := range sample { fmt.Printf("Start Index: %d Value:%s", i, string(letter)) } //Only value fmt.Println("Only value") for _, letter := range sample { fmt.Printf("Value:%s", string(letter)) } //Only index fmt.Println("Only Index") for i := range sample { fmt.Printf("Start Index: %d", i) } } Output: Both Index and Value Start Index: 0 Value:a Start Index: 1 Value:? Start Index: 3 Value:b Only value Value:a Value:? Value:b Only Index Start Index: 0 Start Index: 1 Start Index: 3 for-range loop with a map In case of map for-range iterates over key and values of a map. Below is the format for for-range when using with a map for key, value := range map { //Do something with key and value } A point to be noted that both key and value are optional to be used while using for-range with maps. Let's see a simple code example package main import "fmt" func main() { sample := map[string]string{ "a": "x", "b": "y", } //Iterating over all keys and values fmt.Println("Both Key and Value") for k, v := range sample { fmt.Printf("key :%s value: %s", k, v) } //Iterating over only keys fmt.Println("Only keys") for k := range sample { fmt.Printf("key :%s", k) } //Iterating over only values fmt.Println("Only values") for _, v := range sample { fmt.Printf("value :%s", v) } } Output Both Key and Value key :a value: x key :b value: y Only keys key :a key :b Only values value :x value :y for-range loop with a channel for-range loop works differently too for a channel. For a channel, an index doesn't make any sense as the channel is similar to a pipeline where values enter from one and exit from the other end. So in case of channel, the for-range loop will iterate over values currently present in the channel. After it has iterated over all the values currently present (if any), the for-range loop will not exit but instead wait for next value that might be pushed to the channel and it will exit only when the channel is closed Below is the format when using for-range with channel for value := range channel { //Do something value } Let's see a code example package main import "fmt" func main() { ch := make(chan string) go pushToChannel(ch) for val := range ch { fmt.Println(val) } } func pushToChannel(ch chan Output: a b c Conclusion This is all about for-range loop in golang. Hope you like it. Please share feedback/improvements/mistakes in comments. Next Tutorial ? If ElsePrevious Tutorial ? For Loop The foreach keyword itself does not exist within Go, instead the for loop can be adapted to work in the same manner. The difference however, is by using the range keyword and a for loop together. Like foreach loops in many other languages you have the choice of using the slices' key or value within the loop. Example 1) In our example, we iterate over a string slice and print out each word. As we only need the value we replace the key with an underscore. 1 2 3 4 5 6 7 8 9 10 11 12 13 package main import "fmt" func main() { myList := []string{"dog", "cat", "hedgehog"} // for {key}, {value} := range {list} for _, animal := range myList { fmt.Println("My animal is:", animal) } } Example 2) Likewise, if we want to iterate and loop over each entry in a map, as you would an array, you can in the same way. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 package main import "fmt" func main() { myList := map[string]string{ "dog": "woof", "cat": "meow", "hedgehog": "sniff", } for animal, noise := range myList { fmt.Println("The", animal, "went", noise) } } NEWBEDEVPythonJavascriptLinuxCheat sheet Sometimes the easiest thing to do is the hardest thing to remember... like how to iterate through a string array. :P This is a simple for loop tutorial showing how to iterate over the values inside []string or any kind of arrays. package main import ( "fmt" ) func main() { // taken from divineValues := []string{ "fearlessness", "purification of one's existence", "cultivation of spritual knowledge", "charity", "self-control", "performance of sacrifice", "study of the Vedas", "austerity and simplicity", "non-violence", "truthfulness", "freedom from anger", "renunciation", "tranquility", "aversion to faultfinding", "compassion and freedom from covetousness", "gentleness", "modesty and steady determination", "vigor", "forgiveness", "fortitude", "cleanliness", "freedom from envy and the passion for honor", } for index, each := range divineValues { fmt.Printf("Divine value [%d] is [%s]", index, each) } } IF you gain some knowledge or the information here solved your programming problem. Please consider donating to the less fortunate or some charities that you like. Apart from donation, planting trees, volunteering or reducing your carbon footprint will be great too. Golang Array ExamplesCreate arrays with int and string elements. Iterate over an array with a for-loop.dot net perlsArray. In Go an array is defined by its type, its size and shape. There is no universal array, but many typed and sized arrays. We build methods that act on arrays.Array usage. Slices are more versatile and tend to be used more in Go programs. But arrays can still be useful if we have a fixed size of data.SliceAn example. Let us begin with a simple example that loops over an array of 3 ints. We use an array initializer to create a 3-element array. It contains the values 10, 20 and 30.For We use a for-loop to iterate over the array's elements. In this kind of for-loop, we specify a start, end, and an iteration.Len An array has a length. With len() we access the count of its elements--all elements are counted.LenIndexes The array is indexed starting at 0. The last index is one less than the array's total length.Golang program that uses arraypackage main import "fmt" func main() { // Create an array of three ints. array := [...]int{10, 20, 30} // Loop over three ints and print them. for i := 0; i < len(array); i++ { fmt.Println(array[i]) } } 10 20 30Parameters. We can pass an array (specified by both element count and type) to a method. Arrays are values. They are copied when passed to a method.Caution This is slow. Using slices is faster. For small arrays, passing directly maybe an effective approach.Golang program that passes array as argumentpackage main import "fmt" func display(values [3]int) { fmt.Println(values[0]) fmt.Println(values[1]) fmt.Println(values[2]) } func main() { v := [...]int{5, 10, 15} // Pass the entire array to a method. // ... This copies the array. display(v) } 5 10 15Array slice, method. Usually we pass slices of arrays to methods--this avoids a copy of the elements. Here, display() receives an int array slice.In main We take a full-range slice of the array. The slice contains all the elements in the four-element int array.Golang program that uses slice of array, parameterpackage main import "fmt" func display(values []int) { // Loop over slice argument and display elements. for i:= 0; i < len(values); i++ { fmt.Println(values[i]) } } func main() { // Create a four-element array. array := [...]int{-1, 0, 10, 100} // Pass a slice of the array to display. // ... This slice contains all elements. display(array[:]) } -1 0 10 100Array, slice benchmark. Do arrays have a performance advantage over slices? Potentially, performance information could be used to optimize many programs.Version 1 We use an array: we assign into the array's elements, and then read from the array at indexes.Version 2 In this version of the code, we use a slice. We perform the same actions on the slice that we use on the array.Result The array program has a consistent performance advantage in Go 1.8. Using an array can lead to a significant speedup.Note If you remove the element assignments, there is less of a difference. So an array might be faster only if you are assigning elements.Golang program that benchmarks array, slicepackage main import ( "fmt" "time" ) func main() { // Create array and slice. array := [...]int{10, 20, 30} slice := []int{10, 20, 30} sum := 0 t0 := time.Now() // Version 1: assign into and read array elements. for i := 0; i < 1000000000; i++ { sum = 0 for x := 0; x < len(array); x++ { array[x] = 5 sum += array[x] } if sum == 0 { break } } t1 := time.Now() // Version 2: assign into and read slice elements. for i := 0; i < 1000000000; i++ { sum = 0 for x := 0; x < len(slice); x++ { slice[x] = 5 sum += slice[x] } if sum == 0 { break } } t2 := time.Now() // Results. fmt.Println(t1.Sub(t0)) fmt.Println(t2.Sub(t1)) } 1.3679763s Array: [...]int 1.6191417s Slice: []intArrays versus slices. In Go programs, we typically use slices. But a slice is always based on an array. We can think of arrays as the underlying storage for slices.A summary. Arrays are used as a building block, a foundation, of many things in languages. More complex collections can be built from arrays.? 2007-2021 sam allen. see site info on the changelog A for loop is used to iterate over elements in a variety of data structures (e.g., a slice, an array, a map, or a string). The for statement supports one additional form that uses the keyword range to iterate over an expression that evaluates to an array, slice, map, string, or channel. The basic syntax for a for-range loop is: for index, value := range mydatastructure { fmt.Println(value) } index is the index of the value we are accessing. value is the actual value we have on each iteration. mydatastructure holds the data structure whose values will be accessed in the loop. Note that the above example is highly generalized. The case-by-case examples given below will help you understand the syntax further. Code 1. Iterating over a string The for-range loop can be used to access individual characters in a string. package main import "fmt" func main() { for i, ch := range "World" { fmt.Printf("%#U starts at byte position %d", ch, i) } } The for-range loop can be used to access individual key-value pairs in a map. package main import "fmt" func main() { m := map[string]int{ "one": 1, "two": 2, "three": 3, } for key, value := range m { fmt.Println(key, value) } } For channels, the iteration values are the successive values sent on the channel until its close. package main import "fmt" func main() { mychannel := make(chan int) go func() { mychannel

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