How can I perform case-insensitive sorting of strings in Go using the `sort.Strings()` function?

Case-Insensitive Sorting with sort.Strings() in Go

In Go, it's possible to sort a list of strings in a case-insensitive manner using the sort.Strings() function with a custom comparison function. This custom function compares strings using the results of converting the strings to lowercase.

Example:

<code class="go">data := []string{"A", "b", "D", "c"}
sort.Strings(data) // Default case-sensitive sorting
fmt.Println(data) // Output: [A b c D]</code>

To achieve case-insensitive sorting, we can define the custom function as follows:

<code class="go">sort.Slice(data, func(i, j int) bool {
    return strings.ToLower(data[i]) < strings.ToLower(data[j])
})</code>

This function converts both strings to lowercase before comparing them, resulting in a case-insensitive sorting order.

Running the updated code:

<code class="go">data := []string{"A", "b", "D", "c"}
sort.Slice(data, func(i, j int) bool {
    return strings.ToLower(data[i]) < strings.ToLower(data[j])
})
fmt.Println(data) // Output: [A b c D]</code>

Alternatives:

While the above approach is effective, it can involve string allocations during comparisons. To avoid allocations, an alternative approach is to compare strings rune by rune while converting each rune to lowercase:

<code class="go">func lessLower(sa, sb string) bool {
    for {
        rb, nb := utf8.DecodeRuneInString(sb)
        if nb == 0 {
            return false
        }
        ra, na := utf8.DecodeRuneInString(sa)
        if na == 0 {
            return true
        }
        rb = unicode.ToLower(rb)
        ra = unicode.ToLower(ra)
        if ra != rb {
            return ra < rb
        }
        sa = sa[na:]
        sb = sb[nb:]
    }
}</code>

You can then use this lessLower function to sort the strings case-insensitively:

<code class="go">sort.Slice(data, func(i, j int) bool { return lessLower(data[i], data[j]) })</code>

For language or culture-specific sort orders, consider using the collate package.

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