io.github.privacystreams.commons.item

Class ItemOperators

java.lang.Object

io.github.privacystreams.commons.item.ItemOperators

@PSOperatorWrapper
public class ItemOperators
extends java.lang.Object

A helper class to access common item functions

Constructor Summary

Constructors

Constructor and Description
ItemOperators()

Method Summary

Modifier and Type	Method and Description
static Function<Item,java.lang.Boolean>	containsField(java.lang.String fieldToCheck) Check whether the item contains a given field.
static Function<Item,Item>	excludeFields(java.lang.String... fieldsToExclude) Project an item by excluding some fields.
static <TValue> Function<Item,TValue>	getField(java.lang.String field) Get the value of a given field in the item.
static Function<Item,Item>	getSubItem(java.lang.String subItemField) Get the sub item value of a given field.
static Function<Item,Item>	includeFields(java.lang.String... fieldsToInclude) Project an item by including some fields.
static <TValue> Function<Item,java.lang.Boolean>	isFieldIn(java.lang.String field, TValue[] listToCompare) Check whether the value of a field is in a given list.
static <TValue> Function<Item,Item>	setField(java.lang.String fieldToSet, Function<Item,TValue> fieldValueComputer) Set the value of a new field with a function.
static <TValue> Function<Item,Item>	setField(java.lang.String fieldToSet, TValue fieldValue) Set the value of a new field to a given value.
static <TValue> Function<Item,Item>	setGroupField(java.lang.String fieldToSet, Function<java.util.List<Item>,TValue> fieldValueComputer) Set a field to a new value for each item in the stream.
static <TValue> Function<Item,Item>	setIndependentField(java.lang.String fieldToSet, Function<java.lang.Void,TValue> valueGenerator) Set the value of a new field with a value generator function.
static <Tout> Function<Item,Tout>	wrapSubStreamFunction(Function<java.util.List<Item>,Tout> subStreamFunction) Output the grouped items in the item with a function.
static <Tout> Function<Item,Tout>	wrapValueGenerator(Function<java.lang.Void,Tout> valueGenerator) Wrap a valueGenerator that takes Void as input type to a function that takes Item as input type.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ItemOperators

public ItemOperators()

Method Detail

isFieldIn

public static <TValue> Function<Item,java.lang.Boolean> isFieldIn(java.lang.String field,
                                                                  TValue[] listToCompare)

Check whether the value of a field is in a given list.

Type Parameters:

TValue - the type of list elements

Parameters:

field - the field name

listToCompare - the list to check whether the field is in

Returns:

the predicate

containsField

public static Function<Item,java.lang.Boolean> containsField(java.lang.String fieldToCheck)

Check whether the item contains a given field.

Parameters:

fieldToCheck - the name of field to check

Returns:

the predicate

getField

public static <TValue> Function<Item,TValue> getField(java.lang.String field)

Get the value of a given field in the item.

Type Parameters:

TValue - the type of field value

Parameters:

field - the name of the field to get.

Returns:

the function

wrapSubStreamFunction

public static <Tout> Function<Item,Tout> wrapSubStreamFunction(Function<java.util.List<Item>,Tout> subStreamFunction)

Output the grouped items in the item with a function. This function must be applied to a group item, i.e. must be used after `groupBy` or `localGroupBy`.

Type Parameters:

Tout - the type of sub stream collection result.

Parameters:

subStreamFunction - the function to output sub stream.

Returns:

the function

wrapValueGenerator

public static <Tout> Function<Item,Tout> wrapValueGenerator(Function<java.lang.Void,Tout> valueGenerator)

Wrap a valueGenerator that takes Void as input type to a function that takes Item as input type.

Type Parameters:

Tout - the type of value generator result.

Parameters:

valueGenerator - the function that takes Void as input.

Returns:

the function

setGroupField

public static <TValue> Function<Item,Item> setGroupField(java.lang.String fieldToSet,
                                                         Function<java.util.List<Item>,TValue> fieldValueComputer)

Set a field to a new value for each item in the stream. This transformation can only be used after invoking group methods (`groupBy`, `localGroupBy`, etc.). The value is computed with a function that takes the grouped items as input. Eg. `setGroupField("count", StatisticOperators.count())` will set a new field "count" to each item, which represents the number of items in the grouped sub stream.

Type Parameters:

TValue - the type of the new field value

Parameters:

fieldToSet - the new field name

fieldValueComputer - the function to compute the new field value, which takes the list of grouped items as input.

Returns:

the stream of items with the new field set

setIndependentField

public static <TValue> Function<Item,Item> setIndependentField(java.lang.String fieldToSet,
                                                               Function<java.lang.Void,TValue> valueGenerator)

Set the value of a new field with a value generator function. The value generator function is independent from current item, which does not need a input (Void). The value generator will be evaluated on demand at runtime. For example, `setIndependentField("time", TimeOperators.getCurrentTime())` will set the field "time" to a timestamp in each item; `setIndependentField("wifiStatus", DeviceOperators.isWifiConnected())` will set the field "wifiStatus" to a boolean indicating whether wifi is connected in each item.

Type Parameters:

TValue - the type of the new field value.

Parameters:

fieldToSet - the name of the field to set, it can be a new name or an existing name.

valueGenerator - the function to compute the field value.

Returns:

the item mapper function.

setField

public static <TValue> Function<Item,Item> setField(java.lang.String fieldToSet,
                                                    Function<Item,TValue> fieldValueComputer)

Set the value of a new field with a function.

Type Parameters:

TValue - the type of the new field value.

Parameters:

fieldToSet - the name of the field to set, it can be a new name.

fieldValueComputer - the function to compute the value of the field based on the item.

Returns:

the item mapper function.

setField

public static <TValue> Function<Item,Item> setField(java.lang.String fieldToSet,
                                                    TValue fieldValue)

Set the value of a new field to a given value.

Type Parameters:

TValue - the type of the new field value.

Parameters:

fieldToSet - the name of the field to set, it can be a new name.

fieldValue - the value of the field.

Returns:

the item mapper function.

includeFields

public static Function<Item,Item> includeFields(java.lang.String... fieldsToInclude)

Project an item by including some fields. The fields that are not included will be removed from the item.

Parameters:

fieldsToInclude - the names of the fields to include.

Returns:

the item mapper function.

excludeFields

public static Function<Item,Item> excludeFields(java.lang.String... fieldsToExclude)

Project an item by excluding some fields. The excluded fields will be removed from the item.

Parameters:

fieldsToExclude - the names of the fields to exclude.

Returns:

the item mapper function.

getSubItem

public static Function<Item,Item> getSubItem(java.lang.String subItemField)

Get the sub item value of a given field.

Parameters:

subItemField - the name of sub item field.

Returns:

the function.