Item recommendation could support streaming output, simple format

[jkleint]

Being able to stream recommendations to another process would save the time required to write out and read back in large temp files. Unfortunately, the I/O routines used don't seem to support streaming writes. For example, running item_recommendation with --prediction-file=/dev/stdout crashes with The stream does not support seeking at System.IO.FileStream.SetLength in MyMediaLite.ItemRecommendation.Extensions.WritePredictions. There doesn't seem to be any need for seeking here, but I'm unfamiliar with the .NET I/O subsystem.

It would also be nice to have the output in a form that's easy to parse, say maybe one user item score triple to a line.

[zenogantner]

Will have a look at this.

[zenogantner]

So, there is seeking, because files are not opened for appending by StreamWriter() when using the default constructor. Just opening with the append flag does not seem to work, so I created a fix that uses Mono's Unix API to open files in /dev.

Can you verify the fix, please?

Maybe we should also think about generally offering appending instead of overwriting.
What do you think?

[zenogantner]

I moved the second thing to a separate issue, closing this ticket.
Please re-open if the solution does not work for you.

[jkleint]

Thanks, I will give it a try. If you can write to stdout, you can already append with the shell: >>. No need to complicate the code.