Cover use of multiple input channels

[vdauwera]

Either in Hello World or a generic Part 2 (before Hello GATK)

[adamrtalbot]

One idea here is to replace the UPPER process in hello-world with a ${greeting} ${name}:

e.g.

greetings = Channel.of("hello", "bonjour", "hola")
names = Channel.of("Adam", "Geraldine", "Marcel", "Chris")

greetings.combine(names)

(becomes):

[hello, Adam]
[hello, Geraldine]
[bonjour, Adam]
[bonjour, Geraldine]
[hola, Adam]
[hola, Geraldine]
[hello, Marcel]
[bonjour, Marcel]
[hola, Marcel]
[hello, Chris]
[bonjour, Chris]
[hola, Chris]

The flow could be:

• Introduce name as an idea, with process having two inputs (run: 'hello yourName')
• Run with 1 greeting + 1 name, using 2 channel inputs ✅
• Try and run multiple names, only run 1 because of values vs queue
• Resolve with channels:
  • Change to tuple of val(greeting), val(name)
  • Make a tuple input to process instead of two channels (run: "hello yourName")
  • Use combine to create every combination as above

But this adds considerable time and effort, essentially replacing the existing hello-nextflow module. We could make it a separate module called hello-you between hello-nextflow and hello-gatk.

[vdauwera]

I think I'd rather illustrate this functionality in the context of one or more scientific use cases. I often find myself a little baffled by this type of example because it's so far removed from 'real work' that I have a hard time envisioning how it would apply in a real analysis context.

Generally speaking I'm not keen on putting "here's a thing you can do" exercises into the 'critical path' of the newcomer learning experience unless we can make it obvious why it's a useful/important thing to learn early on.