Converting a text file to Map<String, List> using lambda
13
I am trying to convert the following text input file:
A=groupA1
A=groupA2
A=groupA3
B=groupB1
B=groupB2
into Map<String, List<String>> by splitting each line on "="
So far I manged to get this sort of output:
KEY: A
VALUE: A=groupA1
VALUE: A=groupA2
VALUE: A=groupA3
KEY: B
VALUE: B=groupB1
VALUE: B=groupB2
using such code:
File reqFile = new File("test.config");
try (Stream<String> stream = Files.lines(reqFile.toPath())) {
Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0]));
for (Map.Entry<String, List<String>> entry: conf.entrySet()) {
System.out.println("KEY: " + entry.getKey());
for (String value : entry.getValue()) {
System.out.println("VALUE: " + value);
}
}
} catch (Exception e) {
e.printStackTrace();
}
How to tweak the above lambda to get something like this:
KEY: A
VALUE: groupA1
VALUE: groupA2
VALUE: groupA3
KEY: B
VALUE: groupB1
VALUE: groupB2
java java-8 java-stream
edited Jan 26 at 23:06
Deadpool
6,5392629
asked Jan 26 at 22:43
BartDBartD
685
add a comment |
13
I am trying to convert the following text input file:
A=groupA1
A=groupA2
A=groupA3
B=groupB1
B=groupB2
into Map<String, List<String>> by splitting each line on "="
So far I manged to get this sort of output:
KEY: A
VALUE: A=groupA1
VALUE: A=groupA2
VALUE: A=groupA3
KEY: B
VALUE: B=groupB1
VALUE: B=groupB2
using such code:
File reqFile = new File("test.config");
try (Stream<String> stream = Files.lines(reqFile.toPath())) {
Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0]));
for (Map.Entry<String, List<String>> entry: conf.entrySet()) {
System.out.println("KEY: " + entry.getKey());
for (String value : entry.getValue()) {
System.out.println("VALUE: " + value);
}
}
} catch (Exception e) {
e.printStackTrace();
}
How to tweak the above lambda to get something like this:
KEY: A
VALUE: groupA1
VALUE: groupA2
VALUE: groupA3
KEY: B
VALUE: groupB1
VALUE: groupB2
java java-8 java-stream
edited Jan 26 at 23:06
Deadpool
6,5392629
asked Jan 26 at 22:43
BartDBartD
685
2
much like regular expressions, once you decide to solve a problem with lambdas now you have two problems ( if you do not 100% comprehend what you are doing and why you are doing it that way ). Regular non-lambda solution would be far more efficient and more importantly readable and maintainable.
– Jarrod Roberson
Jan 26 at 22:47
add a comment |
13
13
13
3
I am trying to convert the following text input file:
A=groupA1
A=groupA2
A=groupA3
B=groupB1
B=groupB2
into Map<String, List<String>> by splitting each line on "="
So far I manged to get this sort of output:
KEY: A
VALUE: A=groupA1
VALUE: A=groupA2
VALUE: A=groupA3
KEY: B
VALUE: B=groupB1
VALUE: B=groupB2
using such code:
File reqFile = new File("test.config");
try (Stream<String> stream = Files.lines(reqFile.toPath())) {
Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0]));
for (Map.Entry<String, List<String>> entry: conf.entrySet()) {
System.out.println("KEY: " + entry.getKey());
for (String value : entry.getValue()) {
System.out.println("VALUE: " + value);
}
}
} catch (Exception e) {
e.printStackTrace();
}
How to tweak the above lambda to get something like this:
KEY: A
VALUE: groupA1
VALUE: groupA2
VALUE: groupA3
KEY: B
VALUE: groupB1
VALUE: groupB2
java java-8 java-stream
edited Jan 26 at 23:06
Deadpool
6,5392629
asked Jan 26 at 22:43
BartDBartD
685
I am trying to convert the following text input file:
A=groupA1
A=groupA2
A=groupA3
B=groupB1
B=groupB2
into Map<String, List<String>> by splitting each line on "="
So far I manged to get this sort of output:
KEY: A
VALUE: A=groupA1
VALUE: A=groupA2
VALUE: A=groupA3
KEY: B
VALUE: B=groupB1
VALUE: B=groupB2
using such code:
File reqFile = new File("test.config");
try (Stream<String> stream = Files.lines(reqFile.toPath())) {
Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0]));
for (Map.Entry<String, List<String>> entry: conf.entrySet()) {
System.out.println("KEY: " + entry.getKey());
for (String value : entry.getValue()) {
System.out.println("VALUE: " + value);
}
}
} catch (Exception e) {
e.printStackTrace();
}
How to tweak the above lambda to get something like this:
KEY: A
VALUE: groupA1
VALUE: groupA2
VALUE: groupA3
KEY: B
VALUE: groupB1
VALUE: groupB2
java java-8 java-stream
java java-8 java-stream
edited Jan 26 at 23:06
Deadpool
6,5392629
asked Jan 26 at 22:43
BartDBartD
685
edited Jan 26 at 23:06
Deadpool
6,5392629
asked Jan 26 at 22:43
BartDBartD
685
edited Jan 26 at 23:06
Deadpool
6,5392629
edited Jan 26 at 23:06
Deadpool
6,5392629
edited Jan 26 at 23:06
Deadpool
6,5392629
6,5392629
asked Jan 26 at 22:43
BartDBartD
685
asked Jan 26 at 22:43
BartDBartD
685
asked Jan 26 at 22:43
BartDBartD
685
685
2
much like regular expressions, once you decide to solve a problem with lambdas now you have two problems ( if you do not 100% comprehend what you are doing and why you are doing it that way ). Regular non-lambda solution would be far more efficient and more importantly readable and maintainable.
– Jarrod Roberson
Jan 26 at 22:47
add a comment |
2
much like regular expressions, once you decide to solve a problem with lambdas now you have two problems ( if you do not 100% comprehend what you are doing and why you are doing it that way ). Regular non-lambda solution would be far more efficient and more importantly readable and maintainable.
– Jarrod Roberson
Jan 26 at 22:47
2
2
much like regular expressions, once you decide to solve a problem with lambdas now you have two problems ( if you do not 100% comprehend what you are doing and why you are doing it that way ). Regular non-lambda solution would be far more efficient and more importantly readable and maintainable.
– Jarrod Roberson
Jan 26 at 22:47
much like regular expressions, once you decide to solve a problem with lambdas now you have two problems ( if you do not 100% comprehend what you are doing and why you are doing it that way ). Regular non-lambda solution would be far more efficient and more importantly readable and maintainable.
– Jarrod Roberson
Jan 26 at 22:47
add a comment |
3 Answers
3
active
oldest
votes
10
Map and collect:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(HashMap::new,
(map, item) -> map.computeIfAbsent(item.get(0), k -> new ArrayList<>()).add(item.get(1)),
HashMap::putAll);
Or map and group by:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(Collectors.groupingBy(s -> s.get(0), Collectors.mapping(v->v.get(1), Collectors.toList())));
Stream.collectdocumentation
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
No problem. Mapping solves problem with splitting items two times. I have also added a version with grouping by collectors. If you think it is helpful for you, please, upvote it.
– Michał Ziober
Jan 26 at 23:35
add a comment |
5
Use Collectors.mapping while groupingBy, for more information look at this doc-with-example
Map<String, List<String>> conf = stream.
collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));
System.out.println(conf); //{A=[groupA1, groupA2, groupA3], B=[groupB1, groupB2]}
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
1
That is exactly what I was looking for!Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));and the output:KEY: A VALUE: groupA1 VALUE: groupA2 VALUE: groupA3 KEY: B VALUE: groupB1 VALUE: groupB2
– BartD
Jan 26 at 23:12
add a comment |
2
If you are open to using a third-party library, the following will work using Eclipse Collections.
ListMultimap<String, String> strings = stream
.map(s -> s.split("="))
.collect(Collectors2.toListMultimap(a -> a[0], a -> a[1]));
Collectors2.toListMultimap takes a Function to calculate the key and a separate Function to calculate the value. The ListMultimap<K, V> type is equivalent to Map<K, List<V>>.
Note: I am a committer for Eclipse Collections.
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
10
Map and collect:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(HashMap::new,
(map, item) -> map.computeIfAbsent(item.get(0), k -> new ArrayList<>()).add(item.get(1)),
HashMap::putAll);
Or map and group by:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(Collectors.groupingBy(s -> s.get(0), Collectors.mapping(v->v.get(1), Collectors.toList())));
Stream.collectdocumentation
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
No problem. Mapping solves problem with splitting items two times. I have also added a version with grouping by collectors. If you think it is helpful for you, please, upvote it.
– Michał Ziober
Jan 26 at 23:35
add a comment |
10
Map and collect:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(HashMap::new,
(map, item) -> map.computeIfAbsent(item.get(0), k -> new ArrayList<>()).add(item.get(1)),
HashMap::putAll);
Or map and group by:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(Collectors.groupingBy(s -> s.get(0), Collectors.mapping(v->v.get(1), Collectors.toList())));
Stream.collectdocumentation
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
No problem. Mapping solves problem with splitting items two times. I have also added a version with grouping by collectors. If you think it is helpful for you, please, upvote it.
– Michał Ziober
Jan 26 at 23:35
add a comment |
10
10
10
Map and collect:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(HashMap::new,
(map, item) -> map.computeIfAbsent(item.get(0), k -> new ArrayList<>()).add(item.get(1)),
HashMap::putAll);
Or map and group by:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(Collectors.groupingBy(s -> s.get(0), Collectors.mapping(v->v.get(1), Collectors.toList())));
Stream.collectdocumentation
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
Map and collect:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(HashMap::new,
(map, item) -> map.computeIfAbsent(item.get(0), k -> new ArrayList<>()).add(item.get(1)),
HashMap::putAll);
Or map and group by:
Map<String, List<String>> res = lines.stream()
.map(s -> Arrays.asList(s.split("=")))
.collect(Collectors.groupingBy(s -> s.get(0), Collectors.mapping(v->v.get(1), Collectors.toList())));
Stream.collectdocumentation
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
edited Jan 26 at 23:34
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
answered Jan 26 at 23:15
Michał ZioberMichał Ziober
14.9k1068105
14.9k1068105
No problem. Mapping solves problem with splitting items two times. I have also added a version with grouping by collectors. If you think it is helpful for you, please, upvote it.
– Michał Ziober
Jan 26 at 23:35
add a comment |
No problem. Mapping solves problem with splitting items two times. I have also added a version with grouping by collectors. If you think it is helpful for you, please, upvote it.
– Michał Ziober
Jan 26 at 23:35
No problem. Mapping solves problem with splitting items two times. I have also added a version with grouping by collectors. If you think it is helpful for you, please, upvote it.
– Michał Ziober
Jan 26 at 23:35
No problem. Mapping solves problem with splitting items two times. I have also added a version with grouping by collectors. If you think it is helpful for you, please, upvote it.
– Michał Ziober
Jan 26 at 23:35
add a comment |
5
Use Collectors.mapping while groupingBy, for more information look at this doc-with-example
Map<String, List<String>> conf = stream.
collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));
System.out.println(conf); //{A=[groupA1, groupA2, groupA3], B=[groupB1, groupB2]}
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
1
That is exactly what I was looking for!Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));and the output:KEY: A VALUE: groupA1 VALUE: groupA2 VALUE: groupA3 KEY: B VALUE: groupB1 VALUE: groupB2
– BartD
Jan 26 at 23:12
add a comment |
5
Use Collectors.mapping while groupingBy, for more information look at this doc-with-example
Map<String, List<String>> conf = stream.
collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));
System.out.println(conf); //{A=[groupA1, groupA2, groupA3], B=[groupB1, groupB2]}
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
1
That is exactly what I was looking for!Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));and the output:KEY: A VALUE: groupA1 VALUE: groupA2 VALUE: groupA3 KEY: B VALUE: groupB1 VALUE: groupB2
– BartD
Jan 26 at 23:12
add a comment |
5
5
5
Use Collectors.mapping while groupingBy, for more information look at this doc-with-example
Map<String, List<String>> conf = stream.
collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));
System.out.println(conf); //{A=[groupA1, groupA2, groupA3], B=[groupB1, groupB2]}
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
Use Collectors.mapping while groupingBy, for more information look at this doc-with-example
Map<String, List<String>> conf = stream.
collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));
System.out.println(conf); //{A=[groupA1, groupA2, groupA3], B=[groupB1, groupB2]}
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
edited Jan 26 at 23:12
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
answered Jan 26 at 23:04
DeadpoolDeadpool
6,5392629
6,5392629
1
That is exactly what I was looking for!Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));and the output:KEY: A VALUE: groupA1 VALUE: groupA2 VALUE: groupA3 KEY: B VALUE: groupB1 VALUE: groupB2
– BartD
Jan 26 at 23:12
add a comment |
1
That is exactly what I was looking for!Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList())));and the output:KEY: A VALUE: groupA1 VALUE: groupA2 VALUE: groupA3 KEY: B VALUE: groupB1 VALUE: groupB2
– BartD
Jan 26 at 23:12
1
1
That is exactly what I was looking for!
Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList()))); and the output: KEY: A VALUE: groupA1 VALUE: groupA2 VALUE: groupA3 KEY: B VALUE: groupB1 VALUE: groupB2– BartD
Jan 26 at 23:12
That is exactly what I was looking for!
Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0], Collectors.mapping(v->v.split("=")[1], Collectors.toList()))); and the output: KEY: A VALUE: groupA1 VALUE: groupA2 VALUE: groupA3 KEY: B VALUE: groupB1 VALUE: groupB2– BartD
Jan 26 at 23:12
add a comment |
2
If you are open to using a third-party library, the following will work using Eclipse Collections.
ListMultimap<String, String> strings = stream
.map(s -> s.split("="))
.collect(Collectors2.toListMultimap(a -> a[0], a -> a[1]));
Collectors2.toListMultimap takes a Function to calculate the key and a separate Function to calculate the value. The ListMultimap<K, V> type is equivalent to Map<K, List<V>>.
Note: I am a committer for Eclipse Collections.
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
add a comment |
2
If you are open to using a third-party library, the following will work using Eclipse Collections.
ListMultimap<String, String> strings = stream
.map(s -> s.split("="))
.collect(Collectors2.toListMultimap(a -> a[0], a -> a[1]));
Collectors2.toListMultimap takes a Function to calculate the key and a separate Function to calculate the value. The ListMultimap<K, V> type is equivalent to Map<K, List<V>>.
Note: I am a committer for Eclipse Collections.
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
add a comment |
2
2
2
If you are open to using a third-party library, the following will work using Eclipse Collections.
ListMultimap<String, String> strings = stream
.map(s -> s.split("="))
.collect(Collectors2.toListMultimap(a -> a[0], a -> a[1]));
Collectors2.toListMultimap takes a Function to calculate the key and a separate Function to calculate the value. The ListMultimap<K, V> type is equivalent to Map<K, List<V>>.
Note: I am a committer for Eclipse Collections.
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
If you are open to using a third-party library, the following will work using Eclipse Collections.
ListMultimap<String, String> strings = stream
.map(s -> s.split("="))
.collect(Collectors2.toListMultimap(a -> a[0], a -> a[1]));
Collectors2.toListMultimap takes a Function to calculate the key and a separate Function to calculate the value. The ListMultimap<K, V> type is equivalent to Map<K, List<V>>.
Note: I am a committer for Eclipse Collections.
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
answered Jan 27 at 2:17
Donald RaabDonald Raab
4,33112030
4,33112030
add a comment |
add a comment |
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2
much like regular expressions, once you decide to solve a problem with lambdas now you have two problems ( if you do not 100% comprehend what you are doing and why you are doing it that way ). Regular non-lambda solution would be far more efficient and more importantly readable and maintainable.
– Jarrod Roberson
Jan 26 at 22:47