How to merge maps in Golang and avoid duplicate values?

Merging Maps in Golang

Combining multiple maps into a single merged map in Golang is a common task. Suppose you have three maps:

• map1 = {"id": "id_1", "val": "val_1"}
• map2 = {"id": "id_2", "val": "val_2"}
• map3 = {"id": "id_1", "val": "val_3"}

The goal is to merge these maps based on the id key, resulting in:

• result_map = {"id": "id_1", "val": {"val_1", "val_3"}, "id": "id_2", var: {"val_2"}}

Simple Merge

To merge the maps, you can iterate over each input map and append the values associated with each key to a slice in the result map.

<code class="go">func merge(ms ...map[string]string) map[string][]string {
    res := map[string][]string{}
    for _, m := range ms {
        for k, v := range m {
            res[k] = append(res[k], v)
        }
    }
    return res
}</code>

Avoiding Duplicates

In some cases, you may want to avoid duplicate values in the merged map. To achieve this, check for duplicates before appending.

<code class="go">func merge(ms ...map[string]string) map[string][]string {
    res := map[string][]string{}
    for _, m := range ms {
        srcMap:
        for k, v := range m {
            // Check if (k,v) was added before:
            for _, v2 := range res[k] {
                if v == v2 {
                    continue srcMap
                }
            }
            res[k] = append(res[k], v)
        }
    }
    return res
}</code>

Usage Example

<code class="go">m1 := map[string]string{"id_1": "val_1"}
m2 := map[string]string{"id_2": "val_2", "id_1": "val_1"}
m3 := map[string]string{"id_1": "val_3"}

res := merge(m1, m2, m3)
fmt.Println(res)</code>

Output:

map[id_1:[val_1 val_3] id_2:[val_2]]

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