🚀 The feature

Currently, IterToMap starts to load all data from prior IterDataPipe when the first __getitem__ is invoked here.
https://github.com/pytorch/data/blob/13b574c80e8732744fee6ab9cb7e35b5afc34a3c/torchdata/datapipes/iter/util/converter.py#L78

We can stop loading data from prior IterDataPipe whenever we find the requested index. And, we might need to add a flag to prevent loading data multiple times.

Motivation, pitch

This would improve the performance if users simply iterate over the MapDataPipe as we don't need to pre-load everything at the beginning of the iteration, basically, simulating the behavior of IterDataPipe.

Alternatives

No response

Additional context

No response