\title Concurrent Map and Map-Reduce

Transforming values from a sequence and combining them, all in parallel.

The QtConcurrent::map(), QtConcurrent::mapped() and QtConcurrent::mappedReduced() functions run computations in parallel on the items in a sequence such as a QList. QtConcurrent::map() modifies a sequence in-place, QtConcurrent::mapped() returns a new sequence containing the modified content, and QtConcurrent::mappedReduced() returns a single result.

These functions are part of the \l {Qt Concurrent} framework.

Each of the above functions has a blocking variant that returns the final result instead of a QFuture. You use them in the same way as the asynchronous variants.

QList<QImage> images = ...;
 
// Each call blocks until the entire operation is finished.
QList<QImage> future = QtConcurrent::blockingMapped(images, scaled);
 
QtConcurrent::blockingMap(images, scale);
 
QImage collage = QtConcurrent::blockingMappedReduced(images, scaled, addToCollage);

Note that the result types above are not QFuture objects, but real result types (in this case, QList<QImage> and QImage).