How to search for an element in a golang slice

Question

I have a slice of structs   type Config struct       Key string     Value string       I form a slice of the above struct var myconfig   Config      unmarshal a response body into the above slice if err    json Unmarshal respbody   amp myconfig   err    nil       panic err     fmt Println config    Here is the output of this     key1 test   web key1 test2     How can I search this array to get the element where key  key1

User · Answer

There is no library function for that  You have to code by your own  for    value    range myconfig       if value Key     quot key1 quot               logic          Working code  https   play golang org p IJIhYWROP  package main  import        quot encoding json quot       quot fmt quot     func main         type Config struct           Key   string         Value string            var respbody     byte              quot Key quot   quot Key1 quot    quot Value quot   quot Value1 quot              quot Key quot   quot Key2 quot    quot Value quot   quot Value2 quot                var myconfig   Config      err    json Unmarshal respbody   amp myconfig      if err    nil           fmt Println  quot error  quot   err             fmt Printf  quot   v n quot   myconfig       for    v    range myconfig           if v Key     quot Key1 quot                fmt Println  quot Value   quot   v Value

User · Answer

You can save the struct into a map by matching the struct Key and Value components to their fictive key and value parts on the map   mapConfig    map string string   for    v    range myconfig      mapConfig v Key    v Value     Then using the golang comma ok idiom you can test for the key presence   if v  ok    mapConfig  key1    ok       fmt Printf   s exists   v

User · Answer

With a simple for loop   for    v    range myconfig       if v Key     key1               Found            Note that since element type of the slice is a struct  not a pointer   this may be inefficient if the struct type is  big  as the loop will copy each visited element into the loop variable   It would be faster to use a range loop just on the index  this avoids copying the elements   for i    range myconfig       if myconfig i  Key     key1               Found            Notes   It depends on your case whether multiple configs may exist with the same key  but if not  you should break out of the loop if a match is found  to avoid searching for others    for i    range myconfig       if myconfig i  Key     key1               Found          break           Also if this is a frequent operation  you should consider building a map from it which you can simply index  e g      Build a config map  confMap    map string string   for    v    range myconfig       confMap v Key    v Value       And then to find values by key  if v  ok    confMap  key1    ok          Found

User · Answer

As other guys commented before you can write your own procedure with anonymous function to solve this issue  I used two ways to solve it  func Find slice interface    f func value interface    bool  int       s    reflect ValueOf slice      if s Kind      reflect Slice           for index    0  index  lt  s Len    index                 if f s Index index  Interface                      return index                                   return -1    Uses example  type UserInfo struct       UserId          int    func main         var           destinationList   UserInfo         userId      int   123                destinationList   append destinationList  UserInfo            UserId            23              destinationList   append destinationList  UserInfo            UserId            12                   idx    Find destinationList  func value interface    bool           return value  UserInfo  UserId    userId                 if idx  lt  0           fmt Println  quot not found quot         else           fmt Println idx               Second method with less computational cost  func Search length int  f func index int  bool  int       for index    0  index  lt  length  index             if f index                return index                     return -1    Uses example  type UserInfo struct       UserId          int    func main         var           destinationList   UserInfo         userId      int   123                destinationList   append destinationList  UserInfo            UserId            23              destinationList   append destinationList  UserInfo            UserId            123                   idx    Search len destinationList   func index int  bool           return destinationList index  UserId    userId                 if  idx  lt  0           fmt Println  quot not found quot         else           fmt Println idx

User · Answer

You can use sort Slice   plus sort Search    type Person struct       Name string    func main         crowd      Person   Zoey      Anna      Benni      Chris         sort Slice crowd  func i  j int  bool           return crowd i  Name  lt   crowd j  Name             needle     Benni      idx    sort Search len crowd   func i int  bool           return string crowd i  Name   gt   needle             if crowd idx  Name    needle           fmt Println  Found    idx  crowd idx         else           fmt Println  Found noting     idx            See  https   play golang org p 47OPrjKb0g c

[go] How to search for an element in a golang slice

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