import std.range : walkLength;
auto aes = Aes!(double[], "x", string[], "colour", double[], "alpha")
    ([0.0,1,2,3], ["a","a","b","b"], [0.0,1,0,1]);

assertEqual(group!("colour","alpha")(aes).walkLength,4);
assertEqual(group!("alpha")(aes).walkLength,2);

// Ignores field that does not exist
assertEqual(group!("alpha","abcdef")(aes).walkLength,2);

// Should return one group holding them all
assertEqual(group!("abcdef")(aes)[0].walkLength,4);

assertEqual(group(aes).walkLength,4);

auto aes = Aes!(double[], "x", double[], "y", string[], "colour")([1.0,
    2.0, 1.1], [3.0, 1.5, 1.1], ["a", "b", "a"]);

import std.range : walkLength, front, popFront;

auto grouped = aes.group;
assertEqual(grouped.walkLength, 2);
size_t totalLength = grouped.front.walkLength;
assertGreaterThan(totalLength, 0);
assertLessThan(totalLength, 3);
grouped.popFront;
assertEqual(totalLength + grouped.front.walkLength, 3);