How to remove null values from array containing array

Question

I have an array like this

String arr[][] = {{"abc"}, {"bcd"}, {null}}

This is multi dimensional array (single string array with in an array). I want to remove those nulls and want final result as {{"abc"}, {"bcd"}}. This array could be of any size and there can any number of nulls

I tried something like this. I know I can use traditional for loops, but I want to do it using java8 or more efficiently.

 String arr1[][] = Arrays.stream(arr)
            .filter(str -> (((str != null) && (str.length > 0))))
            .toArray(String[][]::new);

By the way, you should avoid writing arrays like this: String arr1[][], you should write String[][] arr1 instead, for the brackets actually belong to the type, rather than the variable name. The reason it is legal in Java is probably because it is an artifact from C. — MC Emperor
– MC Emperor, Commented Aug 28, 2019 at 5:44

Andronicus · Accepted Answer · 2019-08-28 03:55:02Z

6

You can use streaming from Arrays helper class an filter non-null values:

String arr[][] = {{"abc"}, {"bcd"}, {null}};

String result[][] = Arrays.stream(arr)
    .map(innerArray -> Arrays.stream(innerArray).filter(Objects::nonNull).toArray(String[]::new))
    .toArray(String[][]::new);

Edit:

As @Andreas pointed out, this leaves empty inner arrays, we need to filter them with additional filter(innerArray -> innerArray.length > 0). Finally:

String result[][] = Arrays.stream(arr)
    .map(innerArray -> Arrays.stream(innerArray).filter(Objects::nonNull).toArray(String[]::new))
    .filter(innerArray -> innerArray.length > 0)
    .toArray(String[][]::new);

edited Aug 28, 2019 at 3:55

answered Aug 28, 2019 at 3:48

Andronicus

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6 Comments

Andreas Over a year ago

That produces [[abc], [bcd], []], not the desired [[abc], [bcd]]

Andreas Over a year ago

NullPointerException if input is e.g. {{"abc"}, {"bcd"}, null}

Andronicus Over a year ago

Yes, you're passing a null inner array, for {{"abc"}, {"bcd"}, {null}} it works fine. If you want possibility for null arrays, they would have to be filtered first or null check is needed.

Andreas Over a year ago

Easy enough to add another nonNull filter before the map(...).

Andronicus Over a year ago

That's right, filter(Objects::nonNull) before map would be sufficient. However I won't add it in my answer, as this is not the data in question and adding validation might make the code unreadable. Same thing would happen, when arr == null. But thank you for the discussion :)

|

Oleg Cherednik · Accepted Answer · 2019-08-28 05:13:18Z

0

you're almost there with your solution; just one mistake with a check:

String arr1[][] = Arrays.stream(arr)
                        .filter(str -> str[0] != null)
                        .toArray(String[][]::new);

answered Aug 28, 2019 at 5:13

Oleg Cherednik

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