In many cases, the labels of a Gauge are fixed and known, but sometimes it’s hard to keep track of all labels, for example with an HTTP request collector per endpoint.

It would be very useful to have a method to delete metrics by matching a subset of labels. For example, deleting all metrics with status_code="200" regardless of other labels.

I ran into this issue myself when scraping disk data from multiple instances. On reset I wanted to remove only a specific instance's metrics, but ended up removing all.

The Go client (client_golang) has a DeletePartiallyMatching method.
prometheus/client_golang#834