Syntax question: Idiomatic histograms

[rsaarelm]

I want to make a two-layer histogram structure that accumulates values in bins. Naively, I'd try writing it like this:

struct LogEntry { string day; string task; long duration; }

mut long[string][string] layeredHistogram;
for (entry in log)  // input values from outside the example
    layeredHistogram[entry.day][entry.task] += entry.duration;  // Haha, nope
print("$layeredHistogram");

This doesn't currently work. Should it be made to work or is there a better way to write this idiomatically?

Specifically, there's the expectation of default values here. When a key isn't present in a long valued hashmap, histogram logic expects to pull a 0 (default value for the type) for it. See eg. defaultdict in Python.

[FeepingCreature]

It should work like that. TODO...