I am making a program that converts pictures to a grayscale form and from that grayscale form it converts it to a fairey format.

I am using nested for-loops to convert a nested list. This wo,java,list,lambda,set,java-stream"/>

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I am making a program that converts pictures to a grayscale form and from that grayscale form it converts it to a fairey format.

I am using nested for-loops to convert a nested list. This wo

java - 转换嵌套列表List> 成套

I am making a program that converts pictures to a grayscale form and from that grayscale form it converts it to a fairey format.

I am using nested for-loops to convert a nested list. This wo

问题描述

I am making a program that converts pictures to a grayscale form and from that grayscale form it converts it to a fairey format.

I am using nested for-loops to convert a nested list. This works perfectly but I want to do it using streams and if I do it using that the output changes, but I think it should result in the same output. Where am I wrong?

grayPhoto is a List<List<Graypixel>>

Do any of you see what I'm doing wrong or how the stream should be?

for (int i = 0; i < grayPhoto.size(); i++) {
    for (int j = 0; j < grayPhoto.get(i).size(); j++) {
        numbersSet.add(grayPhoto.get(i).get(j));
    }
}

grayPhoto.forEach(r -> r.forEach(e -> numbersSet.add(e)));

You may wanna look at impyla, the Impala/Hive python client, if you haven't done so already.

As far as the second part of your question, using Impala's SYNC_DDL option will guarantee that DDL changes are propagated across impalads before next DDL is executed.

标签： javalistlambdasetjava-stream

解决方案

您需要使用flatMap操作，将列表列表展平为列表（此处为列表流到流），然后收集为Set：

Set<Graypixel> numbersSet = grayPhoto.stream()
                                     .flatMap(List::stream)
                                     .collect(Collectors.toSet());

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