There is Main three categories for operator in combine

1- Transforming operator

2- Filtering operator

3- Combining operator

1- collction

2- MAP

3- TryMap

4- FlatMap

5- ReplaceNil

6- ReplaceEmpty

7- Scan

1- Filtering basics

2- removeDuplicates

3- Compacting and ignoring

4- IgnoreOutput

5- first(where:)

6- last(where:)

7- Dropping values

 A- Drop(first:)

 B- drop(while:)

 C- drop(untilOutputFrom:)

8- Perfix family

 A- PERFIX()

 B- prefix(while:)

 C- prefix(untilOutputFrom:)

1- Prepending

 A- prepend(Output...)

 B- prepend(Sequence)

 C- prepend(Publisher)

2- Appending

A- append(Output...)

B- append(Sequence)

C- append(Publisher)

3- switchToLatest

3- merge(with:)

5- combineLatest

6- ZIP

https://www.raywenderlich.com/books/combine-asynchronous-programming-with-swift/v2.0