Std::sort on juce::ValueTree

1

Hi,
is it possible to perform a std::sort on a ValueTree?
I got std::find_if to work with a Valuetree, but not std::sort. Is this possible? would be really cool, if not, are there any easy examples for juce::ValueTree::sort ?

Best,
equinox

2

ValueTree features a sort function.

Since ValueTree has begin() and end() iterators I quickly threw a std::sort at it, but the Iterators seemed not to work with std::sort. But could have been my fault)

int main (int argc, char* argv[])
{
    juce::ValueTree tree {"Parent", {},
        {
            {"Node",{{"text", "Ape"}}},
            {"Node",{{"text", "Zebra"}}},
            {"Node",{{"text", "Elephant"}}}
        }};
    
    DBG (tree.toXmlString());

    struct Sorter
    {
        int compareElements (const juce::ValueTree& first, const juce::ValueTree& second)
        {
            return first.getProperty ("text").toString().compare (second.getProperty ("text").toString());
        }
    };
    Sorter sorter;
    tree.sort (sorter, nullptr, false);

// but this didn't compile here:
//    std::sort (tree.begin(), tree.end(), [](const auto& first, const auto& second)
//    {
//        return first.getProperty ("text").toString().compare (second.getProperty ("text").toString());
//    });

    DBG ("sorted:");
    DBG (tree.toXmlString());

    return 0;
}

But the sorter approach did the job

3

std::sort requires that the iterator type is a ā€˜legacy random-access iteratorā€™, but ValueTree::Iterator is only a ā€˜legacy forward iteratorā€™. Therefore, std::sort should not be expected to work with ValueTree iterators.

1 Like
4

Thanks for the example!

    Sorter sorter;
    tree.sort (sorter, nullptr, false);

Could also be

    tree.sort (Sorter(), nullptr, false);

But still longer than some modern std::sort stuff

5

Thanks for the info! Ok, is there any chance that the iterator will be updated (if this is possible at all?).
Otherwise it would be also cool, if juce::ValueTree::sort() would just take some lamdba function.

6

I donā€™t think we have any plans in this area at the moment.

7

Ok, sad to hear.

would be really cool if it would be possible to shortn up those ~8 lines above to:

	tree.sort([](const juce::ValueTree& first, const juce::ValueTree& second) 
		{ return first.getProperty("text").toString().compare(second.getProperty("text").toString()); }, nullptr, false);

But anyway Iā€™m glad that there is also a solution right now.

8

It is possible, with a little helper:

template<typename T>
struct LambdaSorter
{
    LambdaSorter (std::function<int(const T&, const T&)> s) : sortFunc (s) {}
    int compareElements (const T& first, const T& second)
    {
        return sortFunc (first, second);
    }
private:
    std::function<int(const T&, const T&)> sortFunc;
};

int main (int argc, char* argv[])
{
    juce::ValueTree tree {"Parent", {},
        {
            {"Node",{{"text", "Ape"}}},
            {"Node",{{"text", "Zebra"}}},
            {"Node",{{"text", "Elephant"}}}
        }};

    LambdaSorter<juce::ValueTree> sorter ([](const auto& first, const auto& second)
    {
        return first.getProperty ("text").toString().compare (second.getProperty ("text").toString());
    });
    tree.sort (sorter, nullptr, false);
    
    DBG ("sorted:");
    DBG (tree.toXmlString());

    return 0;
}

Your idea to build in place doesnā€™t compile btw, because the ElementComparator is taken by referenceā€¦

Since the sort function is bespoke to the ValueTree you might save the hassle of templating as wellā€¦

Might be a trivial addition to the ValueTree as well, if the juce team wants to add that

9

Cool thanks for your help! With your helper I was able to produce a compiling one-liner :smile:
Helper:

struct LambdaSorter
{
	using Vt = juce::ValueTree;

	LambdaSorter(std::function<int(const Vt&, const Vt&)> s) : sortFunc(s) {}

	int compareElements(const Vt& a, const Vt& b)
	{
		return sortFunc(a, b);
	}
private:
	std::function<int(const Vt&, const Vt&)> sortFunc;
};

Example with one-liner:

	juce::ValueTree tree{ "Parent",
					  {},
					  { { "Node", { { "text", "Ape" } } },
						{ "Node", { { "text", "Zebra" } } },
						{ "Node", { { "text", "Elephant" } } } } };

	DBG(tree.toXmlString());

	tree.sort(LambdaSorter ([](const auto& first, const auto& second) {
		return first.getProperty("text").toString().compare(second.getProperty("text").toString()); }),
		nullptr, false);

	DBG("sorted:");
	DBG(tree.toXmlString());

The Sorted() compiled also on my machine

10

I just cleaned it up a bit and send it to JUCE:

Letā€™s see where it ends up

3 Likes
11

cool! :slight_smile:

12

Little bump, now that the ADC dust has settledā€¦

2 Likes