CODEWITHSUNDEEP
javajava-stream
Vegan Vegeta
Vegan Vegeta

Reputation: 79

Using Java streams to modify some elements and leave some unchanged

I have a use case where I want to modify some entries in a list based on some condition and leave the rest as it is. For this I am thinking of using Java streams but I could not find a solution that will work. I know using filter and map won't work as it will filter out the elements which do not satisfy the condition. Is there something that I can use?

Example:

List<Integer> a = new ArrayList<>();
a.add(1); a.add(2);

// I want to get square of element if element is even 
// Current solution 
List<Integer> b = a.stream().filter(i -> i % 2 == 0).map(i -> i * i).collect(Collectors.toList());

// This outputs - b = [4]
// But I want - b = [1, 4]

Upvotes: 1

Views: 319

Answers (3)

Eritrean
Eritrean

Reputation: 16508

You don't realy need streams and create a new list if all you want is modify some entries. Instead you can use List#replaceAll

a.replaceAll(i -> i % 2 == 0 ? i * i : i);

Upvotes: 1

Mendrika Sandratra
Mendrika Sandratra

Reputation: 555

You can just put the condition in the map like this:

List<Integer> a = new ArrayList<>();
a.add(1);
a.add(2);
List<Integer> b = a.stream().map(i -> i % 2 == 0 ? i * i : i).collect(Collectors.toList());

Upvotes: 0

Chaosfire
Chaosfire

Reputation: 7005

You can make the map operation conditional and remove the filter:

List<Integer> b = a.stream()
            .map(i -> i % 2 == 0 ? i * i : i)
            .collect(Collectors.toList());

Upvotes: 8

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