Level 4: Data shaping · Exercise 58 of 76 · Free

Unflatten dotted keys

A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.

The task

`obj` has dotted keys, like `{ "a.b.c": 1, "a.d": 2 }`, the shape that flattening a nested object produces. Rebuild the nested object: `{ a: { b: { c: 1 }, d: 2 } }`. A key without a dot stays at the top level. Values are kept as they are (an array value stays an array, `undefined` stays `undefined`). Numeric parts like `"k.0"` are still object keys, not array indexes. Keys never conflict (`"a"` and `"a.b"` do not both appear). Do not change `obj`.

What this exercise teaches

Creating an intermediate object only when the key is missing is what lets a.b.c and a.d share the same a. Replacing it on every key throws away what earlier keys built, and turning numeric parts into arrays changes the shape of the result.

A hint if you get stuck

For each key, split on `.`; walk the parts except the last, creating `{}` at each step only when nothing is there yet; then assign the value under the last part.