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Readme for array

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Viktor Lofgren 2023-03-04 19:14:20 +01:00
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libraries/array/readme.md
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@ -31,10 +31,40 @@ array.forEach(0, 100, (pos, val) -> {
## Query Buffers
The library offers many operations for sorting and dealing with sorted data.
Especially noteworthy are the operations `retain()` and `reject()` in
([IntArraySearch](src/main/java/nu/marginalia/array/algo/IntArraySearch.java) and [LongArraySearch](src/main/java/nu/marginalia/array/algo/LongArraySearch.java)) which act upon the
classes [IntQueryBuffer](src/main/java/nu/marginalia/array/buffer/IntQueryBuffer.java)
and [LongQueryBuffer](src/main/java/nu/marginalia/array/buffer/LongQueryBuffer.java);
they keep or remove all items in the buffer that exist in the range. These are used
to offer an intersection operation for the B-Tree that has in practice sub-linear run time.
The classes [IntQueryBuffer](src/main/java/nu/marginalia/array/buffer/IntQueryBuffer.java)
and [LongQueryBuffer](src/main/java/nu/marginalia/array/buffer/LongQueryBuffer.java) are used
heavily in the search engine's query processing.
They are dual-pointer buffers that offer tools for filtering data.
```java
LongQueryBuffer buffer = new LongQueryBuffer(1000);
fillBuffer(buffer);
// A typical filtering operation may look like this:
while (buffer.hasMore()) { // read < end
if (someCondition(buffer.currentValue())) {
// copy the value pointed to by the read
// pointer to the read pointer, and
// advance both
buffer.retainAndAdvance();
}
else {
// advance the read pointer
buffer.rejectAndAdvance();
}
}
// set the read pointer to the read pointer
// after this we can filter again
buffer.finalizeFiltering();
```
Especially noteworthy are the operations `retain()` and `reject()` in
[IntArraySearch](src/main/java/nu/marginalia/array/algo/IntArraySearch.java) and [LongArraySearch](src/main/java/nu/marginalia/array/algo/LongArraySearch.java).
They keep or remove all items in the buffer that exist in the range. These are used
to offer an intersection operation for the B-Tree that has in practice sub-linear run time.