Question

我有一个地图列表形式的数据结构： List< Map<String, List<String>> >

我想使用java 8功能在单个Set中收集列表的所有元素（地图的值）。

示例：

Input:  [ {"a" : ["b", "c", "d"], "b" : ["a", "b"]}, {"c" : ["a", "f"]} ]
Output: ["a", "b", "c", "d", "f"]

感谢。

Answer 1

您可以使用一系列Stream.map和Stream.flatMap：

List<Map<String, List<String>>> input = ...;

Set<String> output = input.stream()    // -> Stream<Map<String, List<String>>>
    .map(Map::values)                  // -> Stream<List<List<String>>>
    .flatMap(Collection::stream)       // -> Stream<List<String>>
    .flatMap(Collection::stream)       // -> Stream<String>
    .collect(Collectors.toSet())       // -> Set<String>
    ;

Answer 2

为此目的使用flatMap

List< Map<String, List<String>> > maps = ...
Set<String> result = maps.stream()
                         .flatMap(m -> m.values().stream())
                         .flatMap(List::stream)
                         .collect(Collectors.toSet());

Answer 3

.flatMap based solutions的替代方法是将这些子迭代融合到最终的collect操作中：

Set<String> output = input.stream()
    .collect(HashSet::new, (set,map) -> map.values().forEach(set::addAll), Set::addAll);

Answer 4

这个问题有很多替代品。以下是一些使用Eclipse Collections容器提供的其他两个答案。

from PyQt4.QtCore import *
from PyQt4.QtGui import *


import sys
import re
import signal
signal.signal(signal.SIGINT, signal.SIG_DFL)


class MyModel(QStandardItemModel):

    def __init__(self, parent=None):
        super(MyModel, self).__init__(parent)

    def data(self, index, role):

        symbol = self.symbol_data[index.row()]
        if role == Qt.DisplayRole:
            return symbol[1]

        elif role == Qt.UserRole:
            return symbol[0]

    def setup(self, data):
        self.symbol_data = data
        for line, name in data:
            item = QStandardItem(name)
            self.appendRow(item)


class MyGui(QDialog):

    def __init__(self, parent=None):

        super(MyGui, self).__init__(parent)

        symbols = [(1, 'cb'), (3, 'cd'), (7, 'ca'), (11, 'aa'), (22, 'bd')]

        model = MyModel()
        model.setup(symbols)

        layout = QVBoxLayout(self)
        self.line = QLineEdit(self)

        layout.addWidget(self.line)

        self.setLayout(layout)

        completer = CustomQCompleter()

        completer.setModel(model)
        completer.setCaseSensitivity(Qt.CaseInsensitive)
        completer.setCompletionMode(QCompleter.UnfilteredPopupCompletion)
        completer.setWrapAround(False)

        self.line.setCompleter(completer)

        self.completer = completer

        self.completer.highlighted[QModelIndex].connect(self.test)

        # QTimer.singleShot(0, self.completer.complete)
        self.line.textChanged[QString].connect(self.pop)

    def pop(self, *x):
        text = x[0]
        self.completer.splitPath(text)
        QTimer.singleShot(0, self.completer.complete)

        self.line.setFocus()

    def test(self, index):
        print 'row in completion model', index.row()
        print 'data:', index.data(Qt.UserRole).toPyObject()

class CustomQCompleter(QCompleter):

    def __init__(self, parent=None):
        super(CustomQCompleter, self).__init__(parent)
        self.local_completion_prefix = ""
        self.source_model = None
        self.first_down = True

    def setModel(self, model):
        self.source_model = model
        self._proxy = QSortFilterProxyModel(
            self, filterCaseSensitivity=Qt.CaseInsensitive)
        self._proxy.setSourceModel(model)
        super(CustomQCompleter, self).setModel(self._proxy)

    def splitPath(self, path):
        self.local_completion_prefix = str(path)
        self._proxy.setFilterFixedString(path)
        return ""

    def eventFilter(self,  obj,  event):

        if event.type() == QEvent.KeyPress:
            'This is used to mute the connection to clear lineedit'
            if event.key() in (Qt.Key_Down, Qt.Key_Up):
                curIndex = self.popup().currentIndex()

                if event.key() == Qt.Key_Down:
                    if curIndex.row() == self._proxy.rowCount()-1:
                        print 'already last row', curIndex.row()
                        if self._proxy.rowCount() == 1:
                            pass
                        else:
                            return True
                else:
                    if curIndex.row() == 0:
                        print 'already first row'
                        return True

                if curIndex.row() == 0 and self.first_down:
                    print 'already row 0 first'
                    self.popup().setCurrentIndex(curIndex)
                    self.first_down = False
                    return True

        super(CustomQCompleter, self).eventFilter(obj,  event)
        return False


if __name__ == '__main__':

    app = QApplication(sys.argv)
    gui = MyGui()
    gui.show()
    sys.exit(app.exec_())

注意：我是Eclipse Collections的提交者。

Java流转换要设置的地图列表

4 个答案: