Golang : Extract or copy items from map based on value



Tags : golang extract-element map-subset copy-map

Problem:

You want to copy map or make a new map with subset or extract items from another map based on certain value. For example, only copy values higher than 200.00 or with string values that match a slice's elements. Kinda like SQL select statement based on certain criteria.

Solution:

The code example below should be self explanatory.

 package main

 import "fmt"

 func main() {

 stockPrices := map[string]float32{
 "IBM":  85.23,
 "HPQ":  399.00,
 "AAPL": 712.00,
 "MSFT": 123.00,
 }

 fmt.Println("---------------------------------------------------------------------------")
 fmt.Println("Original map content")
 fmt.Println("---------------------------------------------------------------------------")

 for k, v := range stockPrices {
 fmt.Printf("key : %v, value : %v \n", k, v)
 }

 fmt.Println("---------------------------------------------------------------------------")
 fmt.Println("New map subset with prices higher than 200")
 fmt.Println("---------------------------------------------------------------------------")

 higherStockPrices := map[string]float32{}

 // copy map value with prices higher than 200
 // to new map

 for name, price := range stockPrices {
 if price > 200.00 {
 fmt.Println(name, price)
 higherStockPrices[name] = price
 }
 }

 //fmt.Println(higherStockPrices)

 for higherName, higherPrice := range higherStockPrices {
 fmt.Printf("key : %v , value : %v \n", higherName, higherPrice)
 }

 fmt.Println("---------------------------------------------------------------------------")
 fmt.Println("New map subset with stock names that are found in slice")
 fmt.Println("---------------------------------------------------------------------------")

 stockNames := []string{"HPQ", "MSFT"}

 for name, price := range stockPrices {
 for _, sName := range stockNames {
 if name == sName {
 fmt.Println(name, price)
 }
 }
 }

 }

Output :

 -------------------------------------------------------------------------------
 Original map content
 -------------------------------------------------------------------------------
 key : IBM, value : 85.23
 key : HPQ, value : 399
 key : AAPL, value : 712
 key : MSFT, value : 123
 -------------------------------------------------------------------------------
 New map subset with prices higher than 200
 -------------------------------------------------------------------------------
 HPQ 399
 AAPL 712
 key : HPQ , value : 399
 key : AAPL , value : 712
 -------------------------------------------------------------------------------
 New map subset with stock names that are found in slice
 -------------------------------------------------------------------------------
 HPQ 399
 MSFT 123

References:

http://blog.golang.org/go-maps-in-action

  See also : Golang : How to delete element(data) from map ?



Tags : golang extract-element map-subset copy-map

By Adam Ng

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