Pratik :
I am trying to group my stream and aggregate on several fields
i.e.
private class Row {
private String sku;
private int colA; // sum
private int colB; // sum
private int colC; // avg
}
Example
sku colA colB colC
---------------------------
ar5sg5h 4 3 4
sd6ad6d 2 5 3
ar5sg5h 6 5 6
sd6ad6d 5 6 3
sd6ad6d 3 7 3
Expected:
sku colA colB colC
---------------------------
ar5sg5h 10 8 5.0
sd6ad6d 10 18 3.0
I already have List<Row> rows, where I have intention to reduce rows with groupBy and aggregation of sum on colA and colB where as average on colC.
How can I achieve this with groupBy + multiple aggregation using Java-8 stream?
YCF_L :
Are you looking to:
List<Row> result = rows.stream()
.collect(Collectors.groupingBy(Row::getSku))
.values().stream()
.map(e -> new Row(e.get(0).getSku(),
e.stream().mapToDouble(Row::getColA).sum(),
e.stream().mapToDouble(Row::getColB).sum(),
e.stream().mapToDouble(Row::getColC).average().getAsDouble()))
.collect(Collectors.toList());
Note: the type int is not helpfull in your case, I would suggest to change it to double as the average is not int.
Outputs
Row(sku=sd6ad6d, colA=10.0, colB=18.0, colC=3.0)
Row(sku=ar5sg5h, colA=10.0, colB=8.0, colC=5.0)
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