Does Go have if x in construct similar to Python

Question

Without iterating over the entire array  how can I check if x in array using Go  Does the language have a construct   Like Python  if  x  in array

User · Answer

The above example using sort is close  but in the case of strings simply use SearchString   files      string  Test conf    util go    Makefile    misc go    main go   target     Makefile  sort Strings files  i    sort SearchStrings files  target  if i  lt  len files   amp  amp  files i     target       fmt Printf  found    s   at files  d  n   files i   i      https   golang org pkg sort  SearchStrings

User · Answer

This is quote from the book  Programming in Go  Creating Applications for the 21st Century       Using a simple linear search like this is the only option for unsorted   data and is fine for small slices  up to hundreds of items   But for   larger slices   especially if we are performing searches repeatedly   the   linear search is very inefficient  on average requiring half the items   to be compared each time       Go provides a sort Search   method which uses the binary search   algorithm  This requires the comparison of only log2 n  items  where n   is the number of items  each time  To put this in perspective  a   linear search of 1000000 items requires 500000 comparisons on average    with a worst case of 1000000 comparisons  a binary search needs at   most 20 comparisons  even in the worst case    files      string  Test conf    util go    Makefile    misc go    main go   target     Makefile  sort Strings files  i    sort Search len files       func i int  bool   return files i   gt   target    if i  lt  len files   amp  amp  files i     target       fmt Printf  found    s   at files  d  n   files i   i      https   play golang org p UIndYQ8FeW

User · Answer

This is as close as I can get to the natural feel of Python s  in  operator  You have to define your own type  Then you can extend the functionality of that type by adding a method like  has  which behaves like you d hope   package main  import  fmt   type StrSlice   string  func  list StrSlice  Has a string  bool       for    b    range list           if b    a               return true                     return false    func main         var testList   StrSlice  The    big    dog    has    fleas        if testList Has  dog             fmt Println  Yay              I have a utility library where I define a few common things like this for several types of slices  like those containing integers or my own other structs   Yes  it runs in linear time  but that s not the point  The point is to ask and learn what common language constructs Go has and doesn t have  It s a good exercise  Whether this answer is silly or useful is up to the reader

User · Answer

Another solution if the list contains static values   eg  checking for a valid value from a list of valid values   func IsValidCategory category string  bool       switch category       case          auto            news            sport            music           return true           return false

User · Answer

There is no built-in operator to do it in Go  You need to iterate over the array  You can write your own function to do it  like this   func stringInSlice a string  list   string  bool       for    b    range list           if b    a               return true                     return false     If you want to be able to check for membership without iterating over the whole list  you need to use a map instead of an array or slice  like this   visitedURL    map string bool        http   www google com   true       https   paypal com   true    if visitedURL thisSite        fmt Println  Already been here

User · Answer

Just had similar question and decided to try out some of the suggestions in this thread   I ve benchmarked best and worst case scenarios of 3 types of lookup    using a map using a list using a switch statement   here s the function code   func belongsToMap lookup string  bool   list    map string bool       900898296857   true       900898302052   true       900898296492   true       900898296850   true       900898296703   true       900898296633   true       900898296613   true       900898296615   true       900898296620   true       900898296636   true    if    ok    list lookup   ok       return true   else       return false       func belongsToList lookup string  bool   list      string       900898296857        900898302052        900898296492        900898296850        900898296703        900898296633        900898296613        900898296615        900898296620        900898296636     for    val    range list       if val    lookup           return true         return false    func belongsToSwitch lookup string  bool   switch lookup   case      900898296857        900898302052        900898296492        900898296850        900898296703        900898296633        900898296613        900898296615        900898296620        900898296636       return true   return false     best case scenarios pick the first item in lists  worst case ones use nonexistant value   here are the results    BenchmarkBelongsToMapWorstCase-4         2000000           787 ns op BenchmarkBelongsToSwitchWorstCase-4     2000000000           0 35 ns op BenchmarkBelongsToListWorstCase-4       100000000           14 7 ns op BenchmarkBelongsToMapBestCase-4          2000000           683 ns op BenchmarkBelongsToSwitchBestCase-4      100000000           10 6 ns op BenchmarkBelongsToListBestCase-4        100000000           10 4 ns op   Switch wins all the way  worst case is surpassingly quicker than best case  Maps are the worst and list is closer to switch   So the moral is  If you have a static  reasonably small list  switch statement is the way to go

User · Answer

Another option is using a map as a set   You use just the keys and having the value be something like a boolean that s always true   Then you can easily check if the map contains the key or not   This is useful if you need the behavior of a set  where if you add a value multiple times it s only in the set once   Here s a simple example where I add random numbers as keys to a map   If the same number is generated more than once it doesn t matter  it will only appear in the final map once   Then I use a simple if check to see if a key is in the map or not   package main  import        fmt       math rand     func main         var MAX int   10      m    make map int bool       for i    0  i  lt   MAX  i             m rand Intn MAX     true            for i    0  i  lt   MAX  i             if    ok    m i   ok               fmt Printf   v is in map n   i            else               fmt Printf   v is not in map n   i                      Here it is on the go playground

[if-statement] Does Go have "if x in" construct similar to Python?

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