CODEWITHSUNDEEP
javajava-stream
prostý člověk
prostý člověk

Reputation: 939

Group By Object Property

I have list of Inventory:

class Inventory {
    String refCode;
    int min;
    int max;
    // getters and setters
}

refCode     min   max
-------    ----  ---
DOUBLE      2   2   
DOUBLE      2   2   
TWIN        1   2   
SINGLE      3   4

Now I wanted to group by using min property so that my output would be like this:

Map<String, int> output;

{DOUBLE=2, TWIN=1, SINGLE=3}

Upvotes: 0

Views: 48

Answers (1)

Samuel Philipp
Samuel Philipp

Reputation: 11042

You can simply use Collectors.toMap() to achieve this:

Map<String, Integer> result = list.stream()
        .collect(Collectors.toMap(Inventory::getRefCode, Inventory::getMin, (a, b) -> a));

This keeps the first value if you have multiple keys. If you want to keep the last one just use (a, b) -> b instead of (a, b) -> a.

If you need the items to be in the same order as the list just use a LinkedHashMap:

Map<String, Integer> result = list.stream()
        .collect(Collectors.toMap(Inventory::getRefCode, Inventory::getMin, (a, b) -> a, LinkedHashMap::new));

Upvotes: 3

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