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());

Answer 1

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

• thiagogcm: 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!

Answer 2

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());