Collect list of list using Java 8 Stream API

Question

I have the following line stream that I read from a file

1 2 4.5

1 6 3 5.5 5.3 6

1 7.2 5 7

How can I collect these lines in a single list of list considering only the Integers? (Notice that within each line the numbers are separated by one or more white spaces)

This is what I tried, but this give me one single list of all integer elements.

        list = reader.lines()
            .map(m -> m.split("\\n"))
            .flatMap(Arrays::stream)
            .map(m -> m.split("\\s+"))
            .flatMap(Arrays::stream)
            .filter(f -> !f.contains("."))
            .map(Integer::parseInt)
            .collect(Collectors.toList());

Vladimir Vagaytsev · Accepted Answer · 2016-10-03 21:19:35Z

6

reader.lines()
   .map(line -> Arrays.stream(line.split("\\s+"))
                      .filter(f -> !f.contains("."))
                      .map(Integer::parseInt)
                      .collect(Collectors.toList())
   .collect(Collectors.toList())

edited Oct 3, 2016 at 21:19

Vladimir Vagaytsev

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answered Oct 3, 2016 at 18:23

Louis Wasserman

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1 Comment

thiagogcm Over a year ago

You're right. lines() is self explanatory. It already return the lines one by one. And I didn't know I could create a new stream inside the map function. Got the strategy! Thanks for the support!

flakes · Accepted Answer · 2016-10-03 18:30:16Z

3

This should do the trick.

list = reader.lines()
    .map(line -> Arrays.stream(line.split("\\s+"))
        .filter(number -> !number.contains("."))
        .map(Integer::parseInt)
        .collect(Collectors.toList()))
    .collect(Collectors.toList());

You may also want to filter for empty lines:

 list = reader.lines()
    .map(line -> Arrays.stream(line.split("\\s+"))
        .filter(number -> !number.contains("."))
        .map(Integer::parseInt)
        .collect(Collectors.toList()))
    .map(l -> !l.isEmpty())
    .collect(Collectors.toList());

answered Oct 3, 2016 at 18:30

flakes

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