LINQ is so fucking useful and well designed feature of .NET ecosystem that it is unreal when you gotta use lang which doesnt have such a thing.
C# design team is/was unparalleled
replies(7):
C# design team is/was unparalleled
It is relatively easy to find similar capabilities in most languages nowadays, unless one is stuck on Go, C and similar.
IEnumerable<> is regular in-memory lambdas/streams, same what you find in many places.
IQueryable<> relies on the LINQ expressions, those CAN be JIT compiled for direct execution, but the fact that they are data-objects is what allows the translation to SQL and execution on the server rather than locally and can give massive gains since processing can be done where the data lives.
Regular transform code in JS (Like IEnumerable)
const ids = users.filter(user => user.age<18).map(user => user.id);
IQueryable like to be transformed to the server:
const ids = users.filter(user => user.age.lt(18)).map(user => user.id);
In C# it'd look identical, but in JS or Java this would be achieved via proxy-object hacks (the .lt() function in the filter instead of the < operator and the .id property getter for the user map to send a flag under the hood for the mapping function).