enumerable

I am a newbie and learning ruby. Would like to have a better understanding of the question asked. I don't understand the use of comparable mixin and enumerable mixin. I mean we don't include these in our class when we need to use them, right? if we want to compare two objects we simply write x > y. Then what is the use of explicitly using them? Great Question Akash! Sometimes it's not "simple" how two objects can be compared! What if you have a Dog class? How do you compare two Dog instances? What should be the comparison based on? Is it enough to compare their name? their breed? their DNA? It

Given a starting number, imagine an infinite sequence of its successive halves. 1, 0.5, 0.25, 0.125, ... (Ignore any numerical instabilities inherent in double .) Can this be done in a single expression without writing any custom extension methods or generator methods? I don't know of a single-expression way but I found this clever generator code here: http://csharpindepth.com/articles/Chapter11/StreamingAndIterators.aspx public static IEnumerable<TSource> Generate<TSource>(TSource start, Func<TSource,TSource> step) { TSource current = start; while (true) { yield return current; current = step

In .NET, both array and list have Enumerable as ancestor, so a method that accept Enumerable as an argument can receive both array and list as its argument. I wonder if there is a similar thing in Java? No, there's no equivalent in Java. I would generally suggest that you design API methods to receive List<T> , Collection<T> or Iterable<T> . While these preclude directly calling the method with an array, you can wrap an array very easily using Arrays.asList . This is more flexible for the caller than specifying an array as a method parameter, which forces a single implementation. I agree it's

I'm trying to create a list of tuples from a list using LINQ, but can't work out how to do it. What I've got is various data in an external file, which I'm reading sections using a standard method into a List<Single> , I then need to turn this into lists of groups of sequential elements of this list (which may have a variable number of elements in the groups). To state it another way: List<Single> with n elements goes to List<Tuple<Single, Single>> with (n/2) elements or List<Single> with n elements goes to List<Tuple<Single, Single, Single>> with (n/3) elements I couldn't work out how to do

I cannot use AsEnumerable() on DataTable, I'm using C# 3 but I'm just targeting 2.0 framework (LINQ capability is courtesy of LINQBridge ). Is there any way I can make DataTable enumerable without using Select() ? bool isExisting = (bdsAttachments.DataSource as DataTable).Select().Any(xxx => (string)dr["filename"] == filename); Update: I wanted it to make it look like this: bool isExisting = (bdsAttachments.DataSource as DataTable).AsEnumerable().Any(xxx => (string)dr["filename"] == filename); I'm getting an inkling that the Select method of DataTable returns a copy, I'm thinking to just use

I'm basicly trying to make my class able to iterate using foreach . I read this tutorial. MSDN . It seems very straight forward. However, I have a problem when I want to iterate second time. I debugged it; and it turned out that it doesn't call the Reset() function. Class A class A : IEnumerable, IEnumerator { int[] data = { 0, 1, 2, 3, 4 }; int position = -1; public object Current { get { return data[position]; } } public bool MoveNext() { position++; return (position < data.Length); } public void Reset() { position = -1; } public IEnumerator GetEnumerator() { return (IEnumerator)this; } }

I have some big fixed-width files and I need to drop the header line. Keeping track of an iterator doesn't seem very idiomatic. # This is what I do now. File.open(filename).each_line.with_index do |line, idx| if idx > 0 ... end end # This is what I want to do but I don't need drop(1) to slurp # the file into an array. File.open(filename).drop(1).each_line do { |line| ... } What's the Ruby idiom for this? If you need it more than once, you could write an extension to Enumerator . class Enumerator def enum_drop(n) with_index do |val, idx| next if n == idx yield val end end end File.open(testfile

HttpServletRequest is using a lot of java.util.Enumeration. I would like to use them in for-each, so i need to convert them into interable. this is not a problem, but I since I have more than one project needing this I need a library to do this. I would rather not make my own - is there any standard library that supports this kind of decoration? Is there a built-in construct to convert an Enumeration to an Iterable? java.util.Collections has a list method that copies an Enumeration into a List , which you can then use in a for-each loop (see javadoc ). Asaf Here is the javadoc from Guava

When I started writing Ruby many years ago, it took me a while to understand the difference between each and map . It only got worse when I discovered all the other Enumerable and Array methods. With the help of the official documentation and many StackOverflow questions , I slowly began to understand what those methods did. Here is what took me even longer to understand though : Why should I use one method or another? Are there any guidelines? I hope this question isn't a duplicate : I'm more interested in the "Why?" than the "What?" or "How?", and I think it could help Ruby newcomers. A more