Develop Reference

Is there a good way to identify whether there is date information contained in a String

I had this problem of trying to identifying whether there is a date information contained in a paragraph. So here are the issues:
We don't know where the date string might appear. A paragraph would be something like "We would like set the appointment at Nov. 15th. Then we would .....". So we cannot directly use DateTime.parse()
The format of the date is arbitrary, it can be more formal forms like "Nov. 15th" or "08/21/1988" or "5th in this month".
It would be unlikely to cover all the cases given that the date information can have various forms, I just want to cover as many cases as possible. The lightweight solution I can come up with would be regular expressions I guess.... And again that would be a huge expression. Does anyone know if there are better solutions or available regular expressions for this?
(P.S. I would prefer more light weighted approaches, methods like machine learning might be more general but is not applicable to my task here)

I'd propably approach it with a regular expression (or multiple) as well.
I'd make the regular expression match regions that look date-like by matching everything around "th", "nd" "st", month/day names and abbreviations, dot/line/slash/colon separated numbers or such things. Experiment with that and see how good it finds dates with a ton of test-cases.
Parsing the possible dates is another story. I guess you'd need something as powerful as PHP's strtotime.
Another approach is to just clearly define a big collection of possible formats. Then, when one is detected, you can easily parse it. Feels too brute-force for me though

As a starting point, there are seven pages of date regexes over at http://regexlib.com. If you don't know which one you're looking for, I would create an array and apply them one at a time. You'll still have a problem with dates like 11/12/2015 vs. 12/11/2015 so some kind of process for clarification is still necessary (e.g., automatically mail back and ask "Do you mean December 11 or November 12?").

Simple physical quantity measurement unit parser for Java

I want to be able to parse expressions representing physical quantities like
g/l
m/s^2
m/s/kg
m/(s*kg)
kg*m*s
°F/(lb*s^2)
and so on. In the simplest way possible. Is it possible to do so using something like Pyparsing (if such a thing exists for Java), or should I use more complex tools like Java CUP?
EDIT: To answere MrD's question the goal is to make conversion between quantities, so for example convert g to kg (this one is simple...), or maybe °F/(kg*s^2) to K/(lb*h^2) supposing h is four hour and lb for pounds

This is harder than it looks. (I have done a fair amount of work here). The main problem is there is no standard (I have worked with NIST on units and although they have finally created a markup language few people use it). So it's really a form of natural language processing and has to deal with :
ambiguity (what does "M" mean - meters or mega)
inconsistent punctuation
abbreviations
symbols (e.g. "mu" for micro)
unclear semantics (e.g. is kg/m/s the same as kg/(m*s)?
If you are just creating a toy system then you should create a BNF for the system and make sure that all examples adhere to it. This will use common punctuation ("/", "", "(", ")", "^"). Character fields can be of variable length ("m", "kg", "lb"). Algebra on these strings ("kg" -> 1000"g" has problems as kg is a fundamental unit.
If you are doing it seriously then ANTLR (#Yaugen) is useful, but be aware that units in the wild will not follow a regular grammar due to the inconsistencies above.
If you are REALLY serious (i.e. prepared to put in a solid month), I'd be interested to know. :-)
My current approach (which is outside the scope of your question) is to collect a large number of examples from the literature automatically and create a number of heuristics.

BigDecimal notation eclipse plugin or nice external tool

I need to make a lot of operations using BigDecimal, and I found having to express
Double a = b - c * d; //natural way
as
BigDecimal a = b.subtract(c.multiply(d))//BigDecimal way
is not only ugly, but a source of mistakes and communication problems between me and business analysts. They were perfectly able to read code with Doubles, but now they can't.
Of course a perfect solution will be java support for operator overloading, but since this not going to happen, I'm looking for an eclipse plugin or even an external tool that make an automatic conversion from "natural way" to "bigdecimal way".
I'm not trying to preprocess source code or dynamic translation or any complex thing, I just want something I can input text and get text, and keep the "natural way" as a comment in source code.
P.S.: I've found this incredible smart hack but I don't want to start doing bytecode manipulation. Maybe I can use that to create a Natural2BigDecimal translator, but I don't want to reinvent the wheel if someone has already done such a tool.
I don't want to switch to Scala/Groovy/JavaScript and I also can't, company rules forbid anything but java in server side code.

"I'm not trying to preprocess source code ... I just want something I can input [bigDecimal arithmetic expression] text".
Half of solving a problem is recognizing the problem for what it is. You exactly want something to preprocess your BigDecimal expressions to produce legal Java.
You have only two basic choices:
A stand-alone "domain specific language" and DSL compiler that accepts "standard" expressions and converts them directly to Java code. (This is one kind of preprocessor). This leaves you with the problem of keeping all the expression fragments around, and somehow knowing where to put them in the Java code.
A tool that reads the Java source text, finds such expressions, and converts them to BigDecimal in the text. I'd suggest something that let you code the expressions outside the actual code and inserted the translation.
Perhaps (stolen from another answer):
// BigDecimal a = b - c * d;
BigDecimal a = b.subtract( c.multiply( d ) );
with the meaning "compile the big decimal expression in the comment into its java equivalent, and replace the following statement with that translation.
To implement the second idea, you need a program transformation system, which can apply source-to-source rewriting rules to transforms (generate as a special case of transform) the code. This is just a preprocessor that is organized to be customizable to your needs.
Our DMS Software Reengineering Toolkit with its Java Front End could do this. You need a full Java parser to do that transformation part; you'll want name and type resolution so that you can parse/check the proposed expression for sanity.
While I agree that the as-is Java notation is ugly, and your proposal would make it prettier, my personal opinion is this isn't worth the effort. You end up with a dependency on a complex tool (yes, DMS is complex: manipulating code isn't easy) for a rather marginal gain.
If you and your team wrote thousands of these formulas, or the writers of such formulas were Java-naive it might make sense. In that case,
I'd go further, and simply insist you write the standard expression format where you need it. You could customize the Java Front End to detect when the operand types were of decimal type, and do the rewriting for you. Then you simply run this preprocessor before every Java compilation step.

I agree, it's very cumbersome! I use proper documentation (comments before each equation) as the best "solution" to this.
// a = b - c * d;
BigDecimal a = b.subtract( c.multiply( d ) )

You might go the route of an expression evaluator. There is a decent (albeit paid) one at http://www.singularsys.com/jep. Antlr has a rudimentary grammar that also does expression evaluation (tho I am not sure how it would perform) at http://www.antlr.org/wiki/display/ANTLR3/Expression+evaluator.
Neither would give you the compile-time safety you would have with true operators. You could also write the various algorithm-based classes in something like Scala, which does support operator overloading out of the box and would interoperate seamlessly with your other Java classes.

Simple java recursive descent parsing library with placeholders

For an application I want to parse a String with arithmetic expressions and variables. Just imagine this string:
((A + B) * C) / (D - (E * F))
So I have placeholders here and no actual integer/double values. I am searching for a library which allows me to get the first placeholder, put (via a database query for example) a value into the placeholder and proceed with the next placeholder.
So what I essentially want to do is to allow users to write a string in their domain language without knowing the actual values of the variables. So the application would provide numeric values depending on some "contextual logic" and would output the result of the calculation.
I googled and did not find any suitable library. I found ANTLR, but I think it would be very "heavyweight" for my usecase. Any suggestions?

You are right that ANTLR is a bit of an overkill. However parsing arithmetic expressions in infix notation isn't that hard, see:
Operator-precedence parser
Shunting-yard algorithm
Algorithms for Parsing Arithmetic Expressions
Also you should consider using some scripting languages like Groovy or JRuby. Also JDK 6 onwards provides built-in JavaScript support. See my answer here: Creating meta language with Java.

If all you want to do is simple expressions, and you know the grammar for those expressions in advance, you don't even need a library; you can code this trivially in pure Java.
See this answer for a detailed version of how:
Is there an alternative for flex/bison that is usable on 8-bit embedded systems?
If the users are defining thier own expression language, if it is always in the form of a few monadic or binary operators, and they can specify the precedence, you can bend the above answer by parameterizing the parser with a list of operators at several levels of precedence.
If the language can be more sophisticated, you might want to investigate metacompilers.

Effective way to handle singular/plural word based on some collection size [closed]

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
We don’t allow questions seeking recommendations for books, tools, software libraries, and more. You can edit the question so it can be answered with facts and citations.
Closed 7 years ago.
Improve this question
There are many instances in my work projects where I need to display the size of some collection in a sentence. For example, if the collection's size is 5, it will say "5 users". If it is size of 1 or 0, it will say "1 user" or "0 user". Right now, I'm doing it with if-else statements to determine whether to print the "s" or not, which is tedious.
I'm wondering if there's an open source JSP custom tag library that allows me to accomplish this. I know I can write one myself... basically, it will have 2 parameters like this: <lib:display word="user" collection="userList" />. Depending on the collection size, it will determine whether to append an "s" or not. But then, this implementation is not going to be too robust because I also need to handle "ies" and some words don't use any of those. So, instead of creating a half-baked tool, I'm hoping there's a more robust library I could utilize right away. I'm not too worried about prefixing the word with is/are in this case.
I use Java, by the way.
Thanks much.

Take a look at inflector, a java project which lets you do Noun.pluralOf("user"), or Noun.pluralOf("user", userList.size()), and which handles a bunch of variations and unusual cases (person->people, loaf->loaves, etc.), as well as letting you define custom mapping rules when necessary.

Hmm, I don't quite see why you need a library for this. I would think the function to do it is trivial:
public String singlePlural(int count, String singular, String plural)
{
return count==1 ? singular : plural;
}
Calls would look like:
singlePlural(count, "user", "users");
singlePlural(count, "baby", "babies");
singlePlural(count, "person", "people");
singlePlural(count, "cherub", "cherubim");
... etc ...
Maybe this library does a whole bunch of other things that make it useful. I suppose you could say that it supplies a dictionary of what all the plural forms are, but in any given program you don't care about the plurals of all the words in the language, just the ones you are using in this program. I guess if the word that could be singular or plural is not known at compile time, if it's something entered by the user, then I'd want a third party dictionary rather than trying to build one myself.
Edit
Suddenly it occurs to me that what you were looking for was a function for making plurals generically, embodying a set of rules like "normally just add 's', but if the word ends in 'y' change the 'y' to 'ies', if it ends in 's' change it to 'ses', ..." etc. I think in English that would be impossible for any practical purpose: there are too many special cases, like "person/people" and "child/children" etc. I think the best you could do would be to have a generic "add an 's'" rule, maybe a few other common cases, and then a long list of exceptions. Perhaps in other languages one could come up with a fairly simple rule.
So as I say, if the word is not known at compile time but comes from some user input, then yes, a third-party dictionary is highly desirable.

This gets complicated in languages other than English, that inflector aims to support in the future.
I am familiar with Czech where user = uživatel and:
1 uživatel
2 uživatelé
3 uživatelé
4 uživatelé
5 uživatelů
...
You can see why programs written with hardcoded singular+plural would get un-i18n-able.
Edit:
Java11 allows you to use the following:
ChoiceFormat fmt = new ChoiceFormat("1#uživatel | 1.0< uživatelé | 4< uživatelů");
System.out.println(fmt.format(1));
System.out.println(fmt.format(4));
System.out.println(fmt.format(5));
ChoiceFormat documentation

This functionality is built into Ruby on Rails. I don't know exactly where, but it should be easy enough to find in the source code, and then you could simply crib the code.
EDIT: Found you some code:
inflector.rb (very helpful comments!)
inflections.rb (extensive word list)
If I remember correctly, it's mainly a matter of appending an "s" to most words, though I believe there is a list (probably hash, err dictionary) of some common exceptions. Notable is the conversion from "person" to "people" :)
You would of course be in for a world of pain if you decided you want to internationalize this to other languages than English. Welcome to the world of highly irregular grammars, and good luck!