I'm not too familiar with Lucene so my apologies if this isn't clear or I'm getting my terms/nomenclature mixed up.
So I have a requirement where a field containing text (example part:123) should be able to be found via the following:
part:123
part 123
part123
Now my understanding of StandardAnalyzer is that it will break the word "part:123" into terms "part" and "123".
So with that, I'm able to search with part:123 or part 123, but because they're two different terms "part123" won't work.
It seems to me like I'd also need to get the indexer to add another term where both are combined, so it'd be "part", "123", "part123".
Is this the right way to accomplish this -- and does anyone know how I'd go about implementing this?
Thanks!
Related
I'm new to lucene, day 1 new. So I've read a tutorial on lucene and spent a while trying to work out how to find a non null value in lucene.
So I have a document called Inspect
The document has two fields I'm interested in: Inspect and Direct.
{
"Inspect": "Feather",
"Direct": {}
}
I want to find all documents where Inspect = "Feather" and Direct is not empty.
I am also interested in finding documents where Direct is also empty.
I am doing this in the ravenDB studio, so I am using lucene. I have tried a few things like
Inspect: Feather
And NOT
Direct: [[NULL_VALUE]]
However this doesn't seem to work. Any advice or some direction would be much appreciated.
Cheers
You need to run a query like this:
Inspect: Feather AND NOT Direct.Count: 0
When you are comparing to a null object, it fails, Direct is not null, but with the .Count there you are actually counting the number of properties in the object, which seems to be what you want.
#stacka Hi! I'm also rather new to RavenDB, but I have some ideas that may help you. First of all, use the '-' (minus) character instead of NOT. It's a convention. Second, you may face the problem that query cannot be run against db, when any property is not indexed. So, you should create one including the field you want to query against. Hope, this would help.
may someone give me a hint on how to index only words with a minimum length using Apache Lucene 5.3.1?
I've searched through the API but didn't find anything which suits my needs except this, but I couldn't figure out how to use that.
Thanks!
Edit:
I guess that's important info, so here's a copy of my explanation of what I want to achieve from my reply below:
"I don't intend to use queries. I want to create a source code summarization tool for which I created a doc-term matrix using Lucene. Now it also shows single- or double-character words. I want to exclude them so they don't show up in the results as they have little value for a summary. I know I could filter them when outputting the results, but that's not a clean solution imo. An even worse would be to add all combinations of single- or double-character words to the stoplist. I am hoping there is a more elegant way then one of those."
You should use a custom Analyzer with LengthTokeFilter. E.g.
Analyzer ana = CustomAnalyzer.builder()
.withTokenizer("standard")
.addTokenFilter("standard")
.addTokenFilter("lowercase")
.addTokenFilter("length", "min", "4", "max", "50")
.addTokenFilter("stop", "ignoreCase", "false", "words", "stopwords.txt", "format", "wordset")
.build();
But it is better to use a stopword (words what occur in almost all documents, like articles for English language) list. This gives a more accurate result.
I am using Lucene to search in a Data-set, I need to now how "" search (I mean exact phrase search) mechanism has been implemented?
I want to make it able to result all "little cat" hits when the user enters "littlecat". I now that I should manipulate the indexing code, but at least I should now how the "" search works.
I want to make it able to result all "little cat" hits when the user enters "littlecat"
This might sound easy but it is very tough to implement. For a human being little and cat are two different words but for a computer it does not know little and cat seperately from littlecat, unless you have a dictionary and your code check those two words in dictionary. On the other hand searching for "little cat" can easily search for "littlecat" aswell. And i believe that this goes beyong the concept of an exact phrase search. Exact phrase search will only return littlecat if you search for "littlecat" and vice versa. Even google seemingly (expectedly too), doesnt return "little cat" on littlecat search
A way to implement this is Dynamic programming - using a dictionary/corpus to compare your individual words against(and also the left over words after you have parsed the text into strings).
Think of it like you were writing a custom spell-checker or likewise. In this, there's also a scenario when more than one combination of words may be left over eg -"walkingmydoginrain" - here you could break the 1st word as "walk", or as "walking" , and this is the beauty of DP - since you know (from your corpus) that you can't form legitimate words from "ingmydoginrain" (ie rest of the string - you have just discovered that in this context - you should pick the segmented word as "Walking" and NOT walk.
Also think of it like not being able to find a match is adding to a COST function that you define, so you should get optimal results - meaning you can be sure that your text(un-separated with white spaces) will for sure be broken into legitimate words- though there may be MORE than one possible word sequences in that line(and hence, possibly also intent of the person seeking this)
You should be able to find pretty good base implementations over the web for your use case (read also : How does Google implement - "Did you mean" )
For now, see also -
How to split text without spaces into list of words?
I am trying to teach myself Lucene.Net to implement on my site. I understand how to do almost everything I need except for one issue. I am trying to figure out how to allow a fuzzy search for all search terms in a search string.
So for example if I have a document with the string The big red fox, I am trying to get bag fix to match it.
The problem is, it seems like in order to perform fuzzy searches, I have to add ~ to every search term the user enters. I am unsure of the best way to go about this. Right now I am attempting this by
string queryString = "bag rad";
queryString = queryString.Replace("~", string.Empty).Replace(" ", "~ ") + "~";
The first replace is due to Lucene.Net throwing an exception if the search string has a ~ already, apparently it can't handle ~~ in a phrase. This method works, but it seems like it will get messy if I start adding fuzzy weight values.
Is there a better way to default all words to allow for fuzzyness?
You might want to index your documents as bi-grams or tri-grams. Take a look at the CJKAnalyzer to see how they do it. You will want to download the source and look at the source.
Following conversion
SELECT to_tsvector('english', 'Google.com');
returns this:
'google.com':1
Why does TSearch2 engine didn't return something like this?
'google':2, 'com':1
Or how can i make the engine to return the exploded string as i wrote above?
I just need "Google.com" to be foundable by "google".
Unfortunately, there is no quick and easy solution.
Denis is correct in that the parser is recognizing it as a hostname, which is why it doesn't break it up.
There are 3 other things you can do, off the top of my head.
You can disable the host parsing in the database. See postgres documentation for details. E.g. something like ALTER TEXT SEARCH CONFIGURATION your_parser_config
DROP MAPPING FOR url, url_path
You can write your own custom dictionary.
You can pre-parse your data before it's inserted into the database in some manner (maybe splitting all domains before going into the database).
I had a similar issue to you last year and opted for solution (2), above.
My solution was to write a custom dictionary that splits words up on non-word characters. A custom dictionary is a lot easier & quicker to write than a new parser. You still have to write C tho :)
The dictionary I wrote would return something like 'www.facebook.com':4, 'com':3, 'facebook':2, 'www':1' for the 'www.facebook.com' domain (we had a unique-ish scenario, hence the 4 results instead of 3).
The trouble with a custom dictionary is that you will no longer get stemming (ie: www.books.com will come out as www, books and com). I believe there is some work (which may have been completed) to allow chaining of dictionaries which would solve this problem.
First off in case you're not aware, tsearch2 is deprecated in favor of the built-in functionality:
http://www.postgresql.org/docs/9/static/textsearch.html
As for your actual question, google.com gets recognized as a host by the parser:
http://www.postgresql.org/docs/9.0/static/textsearch-parsers.html
If you don't want this to occur, you'll need to pre-process your text accordingly (or use a custom parser).