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I want to convert inner map from map of maps.
Old map: Map<String, Map<LocalDate, Integer>> Integer means seconds
New map: Map<String, Map<LocalDate, Duration>>
I have tried created new inner map, but got an error
Error: java: no suitable method found for
putAll(java.util.stream.Stream<java.lang.Object>)methodjava.util.Map.putAll(java.util.Map<? extends java.time.LocalDate,? extends java.time.Duration>)is not applicable
oldMap.entrySet().stream()
.collect(Collectors.toMap(Map.Entry::getKey,
e -> new HashMap<LocalDate, Duration>() {{
putAll(
e.getValue().entrySet().stream()
.map(x -> new HashMap.SimpleEntry<LocalDate, Duration>
(x.getKey(), Duration.ofSeconds(x.getValue())))
);
}}
));
277
Converting complete Map<Key, Value> into Stream: This can be done with the help of Map. entrySet() method which returns a Set view of the mappings contained in this map. In Java 8, this returned set can be easily converted into a Stream of key-value pairs using Set. stream() method.
We can convert a map to a string in java using two array lists. In this, we first fill the map with the keys. Then, we will use keySet() method for returning the keys in the map, and values() method for returning the value present in the map to the ArrayList constructor parameter.
Since our filter condition requires an int variable we first need to convert Stream of String to Stream of Integer. That's why we called the map() function first. Once we have the Stream of Integer, we can apply maths to find out even numbers. We passed that condition to the filter method.
If you want compact code, you may use
Map<String, Map<LocalDate, Duration>> newMap = new HashMap<>();
oldMap.forEach((s,o) -> o.forEach((d, i) ->
newMap.computeIfAbsent(s, x->new HashMap<>()).put(d, Duration.ofSeconds(i))));
If you want to avoid unnecessary hash operations, you may expand it a bit
Map<String, Map<LocalDate, Duration>> newMap = new HashMap<>();
oldMap.forEach((s,o) -> {
Map<LocalDate, Duration> n = new HashMap<>();
newMap.put(s, n);
o.forEach((d, i) -> n.put(d, Duration.ofSeconds(i)));
});
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