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I am looking for useful documentations or examples for the Apache Arrow API. Can anyone point to some useful resources? I was only able to find some blogs and JAVA documentation (which doesn't say much).
From what I read, it is a standard in-memory columnar database for fast analytics. Is it possible to load the data to arrow memory and to manipulate it ?
You should use arrow as a middle man between two applications which need to communicate using passing objects.
Arrow isn’t a standalone piece of software but rather a component used
to accelerate analytics within a particular system and to allow
Arrow-enabled systems to exchange data with low overhead.
For example Arrow improves the performance for data movement within a cluster.
See tests for examples.
#Test
public void test() throws Exception {
BufferAllocator allocator = new RootAllocator(Integer.MAX_VALUE);
File testInFile = testFolder.newFile("testIn.arrow");
File testOutFile = testFolder.newFile("testOut.arrow");
writeInput(testInFile, allocator);
String[] args = {"-i", testInFile.getAbsolutePath(), "-o", testOutFile.getAbsolutePath()};
int result = new FileRoundtrip(System.out, System.err).run(args);
assertEquals(0, result);
validateOutput(testOutFile, allocator);
}
Also Apache Parquet uses it. There are conversion examples from/to arrow objects:
MessageType parquet = converter.fromArrow(allTypesArrowSchema).getParquetSchema();
Schema arrow = converter.fromParquet(supportedTypesParquetSchema).getArrowSchema();
They have some basic documentation on how to use Apache Arrow on their site now. Although it could use a bit of filling out.
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I am looking for a library in java or scala which can do the same clustering like scipy's linkage does.
Performs hierarchical/agglomerative clustering.
The input y may be either a 1d compressed distance matrix or a 2d
array of observation vectors.
If y is a 1d compressed distance matrix, then y must be a (n2)(n2)
sized vector where n is the number of original observations paired in
the distance matrix. The behavior of this function is very similar to
the MATLAB linkage function.
The java libraries I have found (like jblas) are pretty low level lacking of higher order algoritms like linkage. On the other hand I am pretty sure there are some libraries doing that. Would be nice if you could pin point me to one or two.
PS One can find a lot of indviduals implementing some hierarchical clustering, I prefer something more trustable library like commons math if possible. But there I could only find k means clustering.
In the end I am using this library https://github.com/lbehnke/hierarchical-clustering-java
Its not heavyly maintained but passes the comparisment to python and matlab implementations.
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I have a java application. My app makes a call to an external service, then store the data into the database. I want to make it check record in db first, and if not found, make a call to an external service then. I don't want to use hand-made solution for this, I hope there is a library or framework which can do it. I use spring and hibernate 4. What can I do to do that as more gracefully as it possible?
Unless you have tight constraints on the number of calls you can make to the external system, you might want to consider executing both calls at the same time and using whichever responds first.
// Create futures for the two tasks to run concurrently
CompletableFuture<MyObject> checkCache = CompletableFuture.supplyAsync(() -> cache.lookup(key));
CompletableFuture<MyObject> callExternal = CompletableFuture.supplyAsync(() -> externalService.lookup(key));
// run the two operations, and react to the first to complete
checkCache.applyToEither(callExternal,
result -> {
cache.store(key, result);
return result;
})
.applyTo(result -> // do something with the returned value);
This is using Java 8, but you can use Guava, etc, if you're using an earlier version of Java.
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When I can use it, I am a big fan of using Guava's Preconditions. However, the Guava jar is 2 MB, which can be quite sizeable...
I have a project whose jar weighs 26k, therefore the question is, is there a lightweight library having such a utility class, with no dependencies other than the JDK (6+)? While I could create one, I'd rather not reinvent the wheel!
I would use the whole library as suggested in the comments, but if you really want the small size, there is a recommended way specified in guava's docs - Shrinking JARs with ProGuard
You can use valid4j with hamcrest-matchers instead (found on Maven Central as org.valid4j:valid4j).
For input validation (throwing recoverable exception):
import static org.valid4j.Validation.*;
validate(argument, isValid(), otherwiseThrowing(InvalidException.class));
Or for preconditions (like assertions really):
import static org.valid4j.Assertive.*;
require(x, greaterThan(0)); // throws RequireViolation extends AssertionError
Links:
http://www.valid4j.org/
https://github.com/helsing/valid4j
Take a look at the Requirements API that I authored. The upcoming 3.0.0 release weighs in at 167k. It is very well maintained and is very easy to use:
Requirements API
String actual = "foosball";
String expected = "ballroom";
requireThat(actual, "actual").isEqualTo(expected, "expected")
gives you this:
(If your terminal does not support colors, you will get a textual diff instead)
You might want to check Fernando Cejas Arrow Library. It has Preconditions, Guava Strings, Collections, etc.
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In Java, I have set of expressions like cond1 AND (cond2 OR cond3) AND ( cond 4 OR cond5). I would like to convert it into tree and then evaluate the final boolean answer. I tried searching a lot around java BDD but not able to get any. Any suggestion with sample code ?
A 5-second Google search returned some reasonable-looking results:
JavaBDD
Java Decision Diagram Libraries
What is the best Binary Decision Diagram library for Java?
Is this not what you're looking for?
He means Binary Decision Diagrams.
I've been tinkering with JavaBDD and JBDD/JDD. Both are based on BuDDY (a C library) -- JBDD actually uses the C DLLs for a marginal performance boost.
It looks to me like JavaBDD is more fully-featured (ex. it supports composing BDDs, which is what I need). But there is also no tutorial for it, and while the class docs aren't terrible, frankly I can't figure out how to use it for the most basic of boolean operations (like the problem you pose).
JBDD/JDD requires you to use manual garbage collection, and does weird things like store BDD objects in Java integers -- clearly carry-overs from C. But it has a set of tutorials.
If you want to run your own parser, check out JavaCC.
Here is a nice tutorial to get you started. A bit older, but still valid:
http://www.javaworld.com/jw-12-2000/jw-1229-cooltools.html
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I'm looking for a Java library that is capable of performing spatial calculations on sets of lat/lon data. Here are some of the functions that I'm looking for:
Calculate the Great Circle distance between two points
Determine if a point lies within a simple closed polygon, where the polygon is defined by an ordered list of points
Determine if the line between point "A" and point "B" intersects a simple closed polygon, where the polygon is defined by an ordered list of points
Determine if point "A" is within a certain radius of point "B"
What I'm NOT looking for:
I don't want a library that is dependent upon a database geospatial component, such as Oracle Spatial, and cannot function independently.
I don't want a library whose purpose is to generate graphics/maps/etc. I am building an analysis module for an existing application and the end goal is not to create pretty pictures.
I don't want a library for searching large amounts of spatial data. If it also happens to do this, that's ok, but I'm not going to use that feature.
The organization is planning to acquire a license for Oracle Spatial eventually (so spatial searching will be covered at that point), but for now I need to implement the analysis functions that I have mentioned above on small data sets without relying on database-supplied spatial support.
I believe GeoTools would satisfy your requirements. Note that it does have facilities for doing graphics/maps, but they can be left unused easily enough.
There is a new library Spatial4J that seems to fullfill your needs, it supports various spaces and shapes
Spatial4j is a general purpose spatial / geospatial ASL licensed open-source Java library (...)
I haven't used it so far but the README is complete, and repositery is rather popular, and it's available on maven repositery
I was looking for such spatial library when I end up both on the repo and on this question.
Simplelatlng gives more simple API for this:
https://code.google.com/p/simplelatlng/wiki/GettingStarted
In spite of your desire to avoid a library that is used to draw maps, I'd recommend OpenMap. The com.bbn.openmap.geo package of that library does most if not all of the things you are asking for.
I've used STRtree java class to index by lat lng data and distance queries
https://locationtech.github.io/jts/javadoc/org/locationtech/jts/index/strtree/STRtree.html