I have a RichPipe with 3 fields: name: String, time: Long and value: Int. I need to get the value for a specific name, time pair. How can I do it? I can't figure it out from scalding documentation, as it is very cryptic and can't find any examples that do this.
Well a RichPipe is not a Key-Value store, that's why there is no documentation on using as a key-value store :) A RichPipe should be thought of as a pipe - so you can't get at data in the middle without first going in at one end and traversing the pipe till you find the element your looking for. Furthermore this is a little painful in Scalding because you have to write your results to disk (because it's built on top of Hadoop) and then read the result from disk in order to use it in your application. So the code will be something like:
myPipe.filter[String, Long](('name, 'time))(_ == (specificName, specificTime))
.write(Tsv("tmp/location"))
Then you'll need some higher level code to run the job and read the data back into memory to get at the result. Rather than write out all the code to do this (it's pretty straightforward), why don't you give some more context about what your use case is and what you are trying to do - maybe you can solve your problem under the Map-Reduce programming model.
Alternatively, use Spark, you'll have the same problem of having to traverse a distributed dataset, but you don't have the faff of writting to disk and reading back again. Furthermore you can use custom partitioner is Spark that could result in near key-value store like behaviour. But anyway naively, the code would be:
val theValueYouWant =
myRDD.filter {
case (`specificName`, `specificTime`, _) => true
case _ => false
}
.toArray.head._3