welfords online variance algorithm

welford.zig

const std = @import("std");

pub fn main() void {
        const input1 = [_]f32{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
        var mean: f32 = 0;
        var variance: f32 = 0;
        for (input1, 0..) |v, count| {
            const delta = v - mean;
            mean += delta / @as(f32, @floatFromInt(count + 1));
            const delta2 = v - mean;
            variance += delta * delta2;
        }
        const stdev = std.math.sqrt(variance);

        std.debug.print("{[mean]d:0.4} {[stdev]d:0.4}\n", .{
            .mean = mean,
            .stdev = stdev,
        });
}