Collecting occurrences in a HashMap with streams
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I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.
Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:
Map<String, Integer> freq = new HashMap<>();
Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:
foxes.stream()
.map(Fox::getColor)
.forEach()
//...(continued later on);
, where foxes is a List.
My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then
freq.put(Fox::getName, 1)
else
freq.replace(Fox::getName, freq.get(Fox::getName) + 1)
How should I put it together?
java java-8 hashmap java-stream method-reference
edited Jan 4 at 18:49
Jacob G.
16.9k52466
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
add a comment |
I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.
Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:
Map<String, Integer> freq = new HashMap<>();
Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:
foxes.stream()
.map(Fox::getColor)
.forEach()
//...(continued later on);
, where foxes is a List.
My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then
freq.put(Fox::getName, 1)
else
freq.replace(Fox::getName, freq.get(Fox::getName) + 1)
How should I put it together?
java java-8 hashmap java-stream method-reference
edited Jan 4 at 18:49
Jacob G.
16.9k52466
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.
– Naman
Jan 5 at 1:45
add a comment |
I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.
Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:
Map<String, Integer> freq = new HashMap<>();
Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:
foxes.stream()
.map(Fox::getColor)
.forEach()
//...(continued later on);
, where foxes is a List.
My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then
freq.put(Fox::getName, 1)
else
freq.replace(Fox::getName, freq.get(Fox::getName) + 1)
How should I put it together?
java java-8 hashmap java-stream method-reference
edited Jan 4 at 18:49
Jacob G.
16.9k52466
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
I've got an exercise to solve. I've got a Fox class, which has got name and color fields. My exercise is to find the frequency of the foxes by color.
Thus I've created a HashMap, where the String attribute would be the fox name and the Integer would be the occurrence itself:
Map<String, Integer> freq = new HashMap<>();
Having done that, I have been trying to write the code with streams, but I am struggling to do that. I wrote something like this:
foxes.stream()
.map(Fox::getColor)
.forEach()
//...(continued later on);
, where foxes is a List.
My problem is basically with the syntax. I'd like to do something that if the color has no occurrences then
freq.put(Fox::getName, 1)
else
freq.replace(Fox::getName, freq.get(Fox::getName) + 1)
How should I put it together?
java java-8 hashmap java-stream method-reference
java java-8 hashmap java-stream method-reference
edited Jan 4 at 18:49
Jacob G.
16.9k52466
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
edited Jan 4 at 18:49
Jacob G.
16.9k52466
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
edited Jan 4 at 18:49
Jacob G.
16.9k52466
edited Jan 4 at 18:49
Jacob G.
16.9k52466
edited Jan 4 at 18:49
Jacob G.
16.9k52466
16.9k52466
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
asked Jan 4 at 18:43
Csongi NagyCsongi Nagy
19119
19119
IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.
– Naman
Jan 5 at 1:45
add a comment |
IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.
– Naman
Jan 5 at 1:45
IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.
– Naman
Jan 5 at 1:45
IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.
– Naman
Jan 5 at 1:45
add a comment |
1 Answer
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oldest
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I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:
Map<String, Long> result = foxes.stream()
.collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));
This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.
foxes.stream()
.collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));
answered Jan 4 at 18:44
AomineAomine
42.8k74778
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:
Map<String, Long> result = foxes.stream()
.collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));
This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.
foxes.stream()
.collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));
answered Jan 4 at 18:44
AomineAomine
42.8k74778
add a comment |
I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:
Map<String, Long> result = foxes.stream()
.collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));
This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.
foxes.stream()
.collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));
answered Jan 4 at 18:44
AomineAomine
42.8k74778
add a comment |
I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:
Map<String, Long> result = foxes.stream()
.collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));
This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.
foxes.stream()
.collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));
answered Jan 4 at 18:44
AomineAomine
42.8k74778
I wouldn't suggest proceeding with your approach simply because there is already a built in the collector for this i.e. groupingBy collector with counting() as downstream:
Map<String, Long> result = foxes.stream()
.collect(Collectors.groupingBy(Fox::getName, Collectors.counting()));
This finds the frequency by "name", likewise, you can get the frequency by colour by changing the classification function.
foxes.stream()
.collect(Collectors.groupingBy(Fox::getColor, Collectors.counting()));
answered Jan 4 at 18:44
AomineAomine
42.8k74778
edited Jan 4 at 18:48
answered Jan 4 at 18:44
AomineAomine
42.8k74778
answered Jan 4 at 18:44
AomineAomine
42.8k74778
answered Jan 4 at 18:44
AomineAomine
42.8k74778
42.8k74778
add a comment |
add a comment |
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IMHO, the latter part of the question is confusing the initial motive. Mixing up name and color there changes the complete question intent.
– Naman
Jan 5 at 1:45