Java 8 Filter Array Using Lambda
I Have a Double[] and I Want to Filter out (Create a New Array Without) Negative Values in One Line Without Adding for Loops. Is This Possible Using Java 8...
I have a double[] and I want to filter out (create a new array without) negative values in one line without adding for loops. Is this possible using Java 8 lambda expressions?
In python it would be this using generators:
[i for i in x if i > 0]
Is it possible to do something similarly concise in Java 8?
2 Answers
Yes, you can do this by creating a DoubleStream from the array, filtering out the negatives, and converting the stream back to an array. Here is an example:
double[] d = {8, 7, -6, 5, -4};
d = Arrays.stream(d).filter(x -> x > 0).toArray();
//d => [8, 7, 5]
If you want to filter a reference array that is not an Object[] you will need to use the toArray method which takes an IntFunction to get an array of the original type as the result:
String[] a = { "s", "", "1", "", "" };
a = Arrays.stream(a).filter(s -> !s.isEmpty()).toArray(String[]::new);
even simpler, adding up to String[],
use built-in filter filter(StringUtils::isNotEmpty) of org.apache.commons.lang3
import org.apache.commons.lang3.StringUtils;
String test = "a\nb\n\nc\n";
String[] lines = test.split("\\n", -1);
String[] result = Arrays.stream(lines).filter(StringUtils::isNotEmpty).toArray(String[]::new);
System.out.println(Arrays.toString(lines));
System.out.println(Arrays.toString(result));
and output:
[a, b, , c, ]
[a, b, c]
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