Slice chunking in Go

Question

I have a slice with ~2.1 million log strings in it, and I would like to create a slice of slices with the strings being as evenly distributed as possible.

Here is what I have so far:

// logs is a slice with ~2.1 million strings in it.
var divided = make([][]string, 0)
NumCPU := runtime.NumCPU()
ChunkSize := len(logs) / NumCPU
for i := 0; i < NumCPU; i++ {
    temp := make([]string, 0)
    idx := i * ChunkSize
    end := i * ChunkSize + ChunkSize
    for x := range logs[idx:end] {
        temp = append(temp, logs[x])
    }
    if i == NumCPU {
        for x := range logs[idx:] {
            temp = append(temp, logs[x])
        }
    }
    divided = append(divided, temp)
}

The idx := i * ChunkSize will give me the current "chunk start" for the logs index, and end := i * ChunkSize + ChunkSize will give me the "chunk end", or the end of the range of that chunk. I couldn't find any documentation or examples on how to chunk/split a slice or iterate over a limited range in Go, so this is what I came up with. However, it only copies the first chunk multiple times, so it doesn't work.

How do I (as evenly as possible) chunk an slice in Go?

Answer 1

You don't need to make new slices, just append slices of logs to the divided slice.

http://play.golang.org/p/vyihJZlDVy

var divided [][]string

chunkSize := (len(logs) + numCPU - 1) / numCPU

for i := 0; i < len(logs); i += chunkSize {
    end := i + chunkSize

    if end > len(logs) {
        end = len(logs)
    }

    divided = append(divided, logs[i:end])
}

fmt.Printf("%#v\n", divided)