Combine an array of signals into one

[lxian]

Hi,

I have an array of network requests signalProducers and each outputs a string and I would like to combine them into one signalProducer which output an array of string (convert [SignalProducer<String, NSError>] into SignalProducer<[String], NSError>)

I searched and found combineLatest, but it results in a tuple. Is there any way to make it an array ? Thanks in advance.

[andersio]

SignalProducerProtocol.merge and collect should do the job.

[lxian]

@andersio But I want to preserve the ordering of the original array of signalProducers in the combined signalProducer. collect looks like collecting the values in the order that events get fired.

[lxian]

@andersio I write it currently like

arrayOfSignalProducers.reduce(SignalProducer<[String], NSError>.init(value: [])) { (combined, s) in
            return combined.combineLatestWith(s).map({ (arr, str) in
                return arr + [str]
            })
        }

but it looks ugly

[andersio]

You can use the concatenation strategy instead, which would enforce the order. However, you should note that the starting of producer would be serialised too. If you need them to happen in parallel, you might need to use merge and somehow reorder them eventually.

SignalProducer(values: [...]).flatten(.Concat).collect()

[lxian]

@andersio I'm sorry I didn't quit get it. Can you illustrate the flatten approach a bit by some more concrete code ? And I'm using RAC4, should it be flatMap ? Thank you so much !

[andersio]

SignalProducer(values: [producerA, producerB, producerC]).flatten(.Concat) would create a flattened producer, which starts & forward values of producerB after producerA completes, etc.

flatMap is just a shorthand of map + flatten.