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java.lang.Object cascading.pipe.Pipe cascading.pipe.SubAssembly cascading.pipe.assembly.AggregateBy cascading.pipe.assembly.FirstBy
public class FirstBy
Class FirstBy is used to return the first encountered Tuple in a tuple stream grouping.
Typically finding the first Tuple in a tuple stream grouping relies on aGroupBy
and a
First
Aggregator
operation.
If the firstFields
argument has custom Comparator
instances, they will be used
as the GroupBy sortFields
.
This SubAssembly also uses the FirstBy.FirstPartials
AggregateBy.Functor
to collect field values before the GroupBy operator to reduce IO over the network.
This strategy is similar to using combiners
, except no sorting or serialization is invoked and results
in a much simpler mechanism.
The threshold
value tells the underlying FirstPartials functions how many unique key counts to accumulate
in the LRU cache, before emitting the least recently used entry.
AggregateBy
,
Serialized FormNested Class Summary | |
---|---|
static class |
FirstBy.FirstPartials
Class CountPartials is a AggregateBy.Functor that is used to count observed duplicates from the tuple stream. |
Nested classes/interfaces inherited from class cascading.pipe.assembly.AggregateBy |
---|
AggregateBy.CompositeFunction, AggregateBy.Flush, AggregateBy.Functor |
Field Summary |
---|
Fields inherited from class cascading.pipe.assembly.AggregateBy |
---|
AGGREGATE_BY_THRESHOLD |
Fields inherited from class cascading.pipe.Pipe |
---|
configDef, previous, stepConfigDef |
Constructor Summary | |
---|---|
FirstBy(Fields firstFields)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(Fields argumentFields,
Fields firstFields)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(Pipe[] pipes,
Fields groupingFields,
Fields firstFields)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(Pipe[] pipes,
Fields groupingFields,
Fields firstFields,
int threshold)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(Pipe pipe,
Fields groupingFields,
Fields firstFields)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(Pipe pipe,
Fields groupingFields,
Fields firstFields,
int threshold)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(String name,
Pipe[] pipes,
Fields groupingFields,
Fields firstFields)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(String name,
Pipe[] pipes,
Fields groupingFields,
Fields firstFields,
int threshold)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(String name,
Pipe pipe,
Fields groupingFields,
Fields firstFields)
Constructor FirstBy creates a new FirstBy instance. |
|
FirstBy(String name,
Pipe pipe,
Fields groupingFields,
Fields firstFields,
int threshold)
Constructor FirstBy creates a new FirstBy instance. |
Method Summary |
---|
Methods inherited from class cascading.pipe.assembly.AggregateBy |
---|
getAggregators, getArgumentFields, getFunctors, getGroupBy, initialize, initialize, verify |
Methods inherited from class cascading.pipe.SubAssembly |
---|
getConfigDef, getName, getPrevious, getStepConfigDef, getTailNames, getTails, setTails, unwind |
Methods inherited from class cascading.pipe.Pipe |
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equals, getHeads, getTrace, hasConfigDef, hashCode, hasStepConfigDef, isEquivalentTo, named, names, outgoingScopeFor, pipes, print, printInternal, resolveIncomingOperationArgumentFields, resolveIncomingOperationPassThroughFields, toString |
Methods inherited from class java.lang.Object |
---|
clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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@ConstructorProperties(value="firstFields") public FirstBy(Fields firstFields)
AggregateBy
instance.
firstFields
- of type Fields@ConstructorProperties(value={"argumentFields","firstFields"}) public FirstBy(Fields argumentFields, Fields firstFields)
AggregateBy
instance.
firstFields
- of type Fields@ConstructorProperties(value={"pipe","groupingFields","firstFields"}) public FirstBy(Pipe pipe, Fields groupingFields, Fields firstFields)
pipe
- of type PipegroupingFields
- of type FieldsfirstFields
- of type Fields@ConstructorProperties(value={"pipe","groupingFields","firstFields","threshold"}) public FirstBy(Pipe pipe, Fields groupingFields, Fields firstFields, int threshold)
pipe
- of type PipegroupingFields
- of type FieldsfirstFields
- fo type Fieldsthreshold
- of type int@ConstructorProperties(value={"name","pipe","groupingFields","firstFields"}) public FirstBy(String name, Pipe pipe, Fields groupingFields, Fields firstFields)
name
- of type Stringpipe
- of type PipegroupingFields
- of type FieldsfirstFields
- of type Fields@ConstructorProperties(value={"name","pipe","groupingFields","firstFields","threshold"}) public FirstBy(String name, Pipe pipe, Fields groupingFields, Fields firstFields, int threshold)
name
- of type Stringpipe
- of type PipegroupingFields
- of type FieldsfirstFields
- of type Fieldsthreshold
- of type int@ConstructorProperties(value={"pipes","groupingFields","firstFields"}) public FirstBy(Pipe[] pipes, Fields groupingFields, Fields firstFields)
pipes
- of type Pipe[]groupingFields
- of type FieldsfirstFields
- of type Fields@ConstructorProperties(value={"pipes","groupingFields","firstFields","threshold"}) public FirstBy(Pipe[] pipes, Fields groupingFields, Fields firstFields, int threshold)
pipes
- of type Pipe[]groupingFields
- of type FieldsfirstFields
- of type Fieldsthreshold
- of type int@ConstructorProperties(value={"name","pipes","groupingFields","firstFields"}) public FirstBy(String name, Pipe[] pipes, Fields groupingFields, Fields firstFields)
name
- of type Stringpipes
- of type Pipe[]groupingFields
- of type FieldsfirstFields
- of type Fields@ConstructorProperties(value={"name","pipes","groupingFields","firstFields","threshold"}) public FirstBy(String name, Pipe[] pipes, Fields groupingFields, Fields firstFields, int threshold)
name
- of type Stringpipes
- of type Pipe[]groupingFields
- of type FieldsfirstFields
- of type Fieldsthreshold
- of type int
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