Stream merge: Difference between revisions

===Merge two streams===

Optimized for clarity and simplicity, not performance.

===Merge N streams===

{{trans|Phix}}

Of course, as Phix and Nim are very different languages, the code is quite different, but as Phix, we use a priority queue (which is provided by the standard module <code>heapqueue</code>. We work with files built from the “Data” constant, but we destroy them after usage. We have also put the whole merging code in an procedure.

<lang Nim>import heapqueue, os, sequtils, streams

type

Source = tuple[stream: Stream; line: string]

SourceHeap = HeapQueue[Source]

# Comparison of sources. Needed for the heap to sort the sources by line contents.

proc `<`(a, b: Source): bool = a.line < b.line

proc add(heap: var SourceHeap; stream: Stream) =

## Add a stream to the heap.

if stream.atEnd:

stream.close()

else:

heap.push((stream, stream.readLine()))

proc merge(inStreams: seq[Stream]; outStream: Stream) =

## Merge the input streams into an output stream.

# Initialize the heap.

var heap: SourceHeap

for stream in inStreams:

heap.add(stream)

# Merging loop.

while heap.len > 0:

let (stream, line) = heap.pop()

outStream.writeLine line

heap.add(stream)

when isMainModule:

const

Data = ["Line 001\nLine 008\nLine 017\n",

"Line 019\nLine 033\nLine 044\nLine 055\n",

"Line 019\nLine 029\nLine 039\n",

"Line 023\nLine 030\n"]

Filenames = ["file1.txt", "file2.txt", "file3.txt", "file4.txt"]

# Create files.

for i, name in Filenames:

writeFile(name, Data[i])

# Create input and output streams.

let inStreams = Filenames.mapIt(Stream(newFileStream(it)))

let outStream = Stream(newFileStream(stdout))

# Merge the streams.

merge(inStreams, outStream)

# Clean-up: delete the files.

for name in Filenames:

removeFile(name)</lang>

{{out}}

<pre>Line 001

Line 008

Line 017

Line 019

Line 019

Line 023

Line 029

Line 030

Line 033

Line 039

Line 044

Line 055</pre>