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• Finding the maximum number of child nodes in a tree

  - by Jiminizer

  First, I should make it clear that this is required for an academic project. I am trying to find the maximum number of child nodes for any node in a tree, using Common Lisp. My current code is shown below - I'm not 100% on the logic of it, but I feel it should work, however it isn't giving me the required result. (defun breadth (list y) (setf l y) (mapcar #'(lambda (element) (when (listp element) (when (> (breadth element (length element)) l) (setf l (breadth element (length element))) ))) list) l) (defun max-breadth(list) (breadth list (length list)) ) As an example, running (max-breadth '(a ( (b (c d)) e) (f g (h i) j))) should return 4. Does anyone have any ideas where I'm going wrong? I suspect it's related to the second conditional, but I'm not sure.

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• Rails 2.3.x, named_scope chaining with INNER JOIN complication

  - by randombits

  I have two hypothetical classes, Foo and Bar. Foo contains many Bars. Bar can only belong to one Foo. Ultimately the SQL query I'm trying to make happen looks like the following: SELECT * from bar INNER JOIN foo ON bar.foo_id = foo.id where bar.in_use = 0 and bar.customer_id = 1 and foo.category = 0 That query does what I need. Now I'm trying to break the problem down in Rails using chained named_scopes. First, the straight forward in_use and customer_id scopes I have set: named_scope :available, :conditions => { :in_use => 0 } named_scope :not_available, :conditions => { :in_use => 1 } named_scope :customer, lambda { |num| { :conditions => { :customer_id => num } } } Now the part I'm stuck at, is I'm trying to do something like this in my code: abar = Bar.available.customer(1).category(0) how and where do I put the category named_scope to make this work?

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• Specify an inline callback function as an argument.

  - by Matthias Vance

  LS, Let me first explain what I'm trying to achieve using some pseudo-code (JavaScript). // Declare our function that takes a callback as as an argument, and calls the callback with true. B(func) { func(true); } // Call the function B(function(bool success) { /* code that uses success */ }); I hope this says it all. If not, please comment on my question so I can write a little more to clarify my issue. What I want is to have code like this in C++. I have tried to use lambda functions, but I was unable to specify a parameter type for those. Kind regards, Matthias Vance

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• LINQ Searching Only Allowing Equivalency

  - by Mad Halfling

  Hi folks, I'm trying to filter a set of records based on a sub-object's criteria. This compiles ok recordList = recordList.Where(r => r.Areas.Where(a => a.Area == "Z").Count() > 0); but this doesn't recordList = recordList.Where(r => r.Areas.Where(a => a.Area <= "Z").Count() > 0); giving these errors Cannot convert lambda expression to type 'string' because it is not a delegate type Delegate 'System.Func' does not take '1' arguments Operator '<=' cannot be applied to operands of type 'string' and 'string' != works ok, by any sort of less than or greater than operation fails.

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• Equivalents of Java and .NET technologies/frameworks

  - by Paul Sasik

  I work in a shop that is a mix of mostly Java and .NET technologists. When discussing new solutions and architectures we often encounter impedance in trying to compare the various technologies, frameworks, APIs etc. in use between the two camps. It seems that each camp knows little about the other and we end up comparing apples to oranges and forgetting about the bushels. While researching the topic I found this: Java -- .Net rough equivalents It's a nice list but it's not quite exhaustive and is missing the key .NET 3.0 technologies and a few other tidbits. To complete that list: what are the near/rough equivalents (or a combination of technologies) in Java to the following in .NET? WCF WPF Silverlight WF Generics Lambda expressions Linq (not Linq-to-SQL) TPL F# IronPython IronRuby ...have i missed anything else? Note that I omitted technologies that are already covered in the linked article. I would also like to hear feedback on whether the linked article is accurate. Thanks.

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• Using numpy.apply

  - by andylei

  What's wrong with this snippet of code? import numpy as np from scipy import stats d = np.arange(10.0) cutoffs = [stats.scoreatpercentile(d, pct) for pct in range(0, 100, 20)] f = lambda x: np.sum(x > cutoffs) fv = np.vectorize(f) # why don't these two lines output the same values? [f(x) for x in d] # => [0, 1, 2, 2, 3, 3, 4, 4, 5, 5] fv(d) # => array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0]) Any ideas?

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• Need to debug LINQ simple queries in Visual Studio 2010

  - by maxima120

  I often get in a position when I need to know why my LINQ doesnt work as intended... I use object collections and extensions. I dont want spend more than couple of minutes on it. LINQ supposed to make developer's life easier not harder. I hoped VS 2010 will have it fixed but I now use RC and it still doesnt let me type LINQ and check what is going on... Says as before "Expression cannot contain lambda expressions"... Is there some add-on for Visual Studio so I can quickly and effectively run ad-hoc queries and find out what is going on and where I am wrong?

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• 'Generic' ViewModel

  - by Ian MacPherson

  Using EF 4, I have several subtypes of a 'Business' entity (customers, suppliers, haulage companies etc). They DO need to be subtypes. I am building a general viewmodel which calls into a service from which a generic repository is accessed. As I have 4 subtypes, it would be good to have a 'generic' viewmodel used for all of these. Problem is of course is that I have to call a specific type into my generic repository, for example: BusinessToRetrieve = _repository .LoadEntity<Customer>(o => o.CustomerID == customerID); It would be good to be able to call <SomethingElse>, somethingElse being one or other of the subtypes), otherwise I shall have to create 4 near identical viemodels, which seems a waste of course! The subtype entity name is available to the viewmodel but I've been unable to figure out how to make the above call convert this into a type. An issue with achieving what I want is that presumably the lambda expression being passed in wouldn't be able to resolve on a 'generic' call ?

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• Using local classes with STL algorithms

  - by David Rodríguez - dribeas

  I have always wondered why you cannot use locally defined classes as predicates to STL algorithms. In the question: Approaching STL algorithms, lambda, local classes and other approaches, BubbaT mentions says that 'Since the C++ standard forbids local types to be used as arguments' Example code: int main() { int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; std::vector<int> v( array, array+10 ); struct pair : public std::unary_function<int,bool> { bool operator()( int x ) { return !( x % 2 ); } }; std::remove_if( v.begin(), v.end(), pair() ); // error } Does anyone know where in the standard is the restriction? What is the rationale for disallowing local types?

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• Multiple range product in Python

  - by Tyr

  Is there a better way to do this: perms = product(range(1,7),range(1,7),range(1,7)) so that I can choose how many ranges I use? I want it to be equivalent to this, but scalable. def dice(num) if num == 1: perms = ((i,) for i in range(1,7)) elif num == 2: perms = product(range(1,7),range(1,7)) elif num == 3: perms = product(range(1,7),range(1,7),range(1,7)) #... and so on but I know there has to be a better way. I'm using it for counting dice outcomes. The actual code def dice(selection= lambda d: d[2]): perms = itertools.product(range(1,7),range(1,7),range(1,7)) return collections.Counter(((selection(sorted(i)) for i in perms))) where I can call it with a variety of selectors, like sum(d[0:2]) for the sum of the lowest 2 dice or d[1] to get the middle dice.

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• Rough/near equivalents of Java and .NET technologies/frameworks

  - by Paul Sasik

  I work in a shop that is a mix of mostly Java and .NET technologists. When discussing new solutions and architectures we often encounter impedance in trying to compare the various technologies, frameworks, APIs etc. in use between the two camps. It seems that each camp knows little about the other and we end up comparing apples to oranges and forgetting about the bushels. While researching the topic I found this: Java -- .Net rough equivalents It's a nice list but it's not quite exhaustive and is missing the key .NET 3.0 technologies and a few other tidbits. To complete that list: what are the near/rough equivalents (or a combination of technologies) in Java to the following in .NET? WCF WPF Silverlight WF Generics Lambda expressions Linq (not Linq-to-SQL) ...have i missed anything else? Note that I omitted technologies that are already covered in the linked article. I would also like to hear feedback on whether the linked article is accurate. Thanks. (Will CW if requested.)

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• How can I make named_scope in Rails return one value instead of an array?

  - by sameera207

  I want to write a [named scope] to get a record from its id. For example, I have a model called Event, and I want to simulate Event.find(id) with use of named_scope for future flexibility. I used this code in my model: named_scope :from_id, lambda { |id| {:conditions => ['id= ?', id] } } and I call it from my controller like Event.from_id(id). But my problem is that it returns an array of Event objects instead of just one object. Thus if I want to get event name, I have to write event = Event.from_id(id) event[0].name while what I want is event = Event.from_id(id) event.name Am I doing something wrong here?

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• Whats the significance of named scope in rails?

  - by piemesons

  Before going for details. Question 1:-- Whats the meaning of scope here (ie named scope)? whats the benefits of using named scope? Now:- from agile development with rails book:-- class Order < ActiveRecord::Base named_scope :last_n_days, lambda { |days| {:conditions => ['updated < ?' , days] } } named_scope :checks, :conditions => {:pay_type => :check} end Such a named scope would make finding the last weeks worth of orders a snap. orders = Orders.last_n_days(7) Scopes can also be combined orders = Orders.checks.last_n_days(7) why we are using named_scope here. We can do the same using methods. Whats special thing we got using named_scope.

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• EF Code First - Include(x => x.Properties.Entity) a 1 : Many association

  - by VulgarBinary

  Given a EF-Code First CTP5 entity layout like: public class Person { ... } which has a collection of: public class Address { ... } which has a single association of: public class Mailbox { ... } I want to do: PersonQuery.Include(x => x.Addresses).Include("Addresses.Mailbox") WITHOUT using a magic string. I want to do it using a lambda expression. I am aware what I typed above will compile and will bring back all Persons matching the search criteria with their addresses and each addresses' mailbox eager loaded, but it's in a string which irritates me. How do I do it without a string? Thanks Stack!

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• How to use/manipulate return value from nested boost::bind

  - by JQ

  I have two functions: 1. A & DataSource(); 2. void DataConsumer( A * ); What I want to achieve: Using one statement to assemble them into one functor. I have tried: 1. boost::function< void() func( boost::bind( DataConsumer, & boost::bind( DataSource ) ) ); certainly it didn't work, compiler says it can not convert 'boost::_bi::bind_t ' to 'A *' 2. boost::function< void() func( boost::bind( DataConsumer, boost::addressof( boost::bind( DataSource ) ) )); compiler says cannot convert parameter 1 from 'boost::_bi::bind_t' to 'A &' Question: how to use return value from the nested boost::bind ? or if you want to use boost::lambda::bind.

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• How to compile scheme into native binary files ?

  - by Joe

  I am very new to scheme. And now I am trying to compile some scheme code into binary file which will be loaded faster into interpreter. (The interpreter is a hybrid interpreter)Some one told me that I can compile the code into native binary file and then load it into interperter. And my question is: 1. What is the native binary file? 2. How can I compile the scheme code into a native binary file? 3. How can I load native bianry file into scheme interpreter? Thanks in advance. Joe Suggested that I want to compile below code into native binary file: (define test (lambda() (display "this is a test")) And then load the bianry file into interpreter and call the function "test".

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• Sorting objects in Python

  - by Curious2learn

  I want to sort objects using by one of their attributes. As of now, I am doing it in the following way USpeople.sort(key=lambda person: person.utility[chosenCar],reverse=True) This works fine, but I have read that using operator.attrgetter() might be a faster way to achieve this sort. First, is this correct? Assuming that it is correct, how do I use operator.attrgetter() to achieve this sort? I tried, keyFunc=operator.attrgetter('utility[chosenCar]') USpeople.sort(key=keyFunc,reverse=True) However, I get an error saying that there is no attribute 'utility[chosenCar]'. The problem is that the attribute by which I want to sort is in a dictionary. For example, the utility attribute is in the following form: utility={chosenCar:25000,anotherCar:24000,yetAnotherCar:24500} I want to sort by the utility of the chosenCar using operator.attrgetter(). How could I do this? Thanks in advance.

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• Call a function by its name, given from string java

  - by Joao

  Hello, I would like to be able to call a function based on its name provided by a string. Something like public void callByName(String funcName){ this.(funcName)(); } I have searched a bit into lambda funcions but they are not supported. I was thinking about going for Reflection, but I am a bit new to programming, so I am not so familiar with the subject. This whole question was brought up on my java OOP class, when I started GUI (Swing, swt) programming, and events. I found that using object.addActionCommand() is very ugly, because I would later need to make a Switch and catch the exact command I wanted. I would rather do something like object.attachFunction(btn1_click), so that it would call the btn1_click function when the event click was raised. Thank you Joao

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• appcfg.py upload_data entity kind problem

  - by Dingo

  Hi, I am developing application on app-engine-path and I would like to upload some data to datastore. For example I have a model models/places.py: class Place(db.Model): name = db.StringProperty() longitude = db.FloatProperty() latitude = db.FloatProperty() If I save this in view, kind() of this entity is "models_place". All is ok, Place.all() in view work fine. But: If I upload some next row using appcfg.py upload_data, the kind() of this entities is Place. loader.py look like this: import datetime, os, sys from google.appengine.ext import db from google.appengine.tools import bulkloader libs_path = os.path.join("/home/martin/myproject/src/") if libs_path not in sys.path: sys.path.insert(0, libs_path) from models import places class AlbumLoader(bulkloader.Loader): def __init__(self): bulkloader.Loader.__init__(self, 'Place', [('name', lambda x: x.decode('utf-8')), ('longitude', float), ('latitude', float), ]) loaders = [AlbumLoader] and command for uploading: python /usr/local/google_appengine/appcfg.py upload_data --config_file=places_loader.py --kind=models_place --filename=data/places.csv --url=http://localhost:8000/remote_api /home/martin/myproject/src/

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• Where and which data to save into session on an ASP.NET MVC 2 application?

  - by Shaharyar

  I am having some trouble saving the state of my current view. Currenly I have several selectlist calling their own Action method on the controller that returns the Index view with the filtered model based on the values of the selectlist. I have also written a little FileResult action that creates a csv file based on the current model. But I am only covering one selectlist right now as I only save the value of selectList1 into the session and access it with Session["SelectListValue1"] What are the best practices in this situation? Should I redo the entire (each action for each SelectList) part? Should I save each SelectLists value into the session and check if it's null? Or should I just save the Lambda Expression into the session and modify it during every call?

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• C# -Interview Question Anonymous Type

  - by Amutha

  Recently i was asked to prove the power of C# 3.0 in a single line( might be tricky) i wrote new int[] { 1, 2, 3 }.Union(new int[]{10,23,45}). ToList().ForEach(x => Console.WriteLine(x)); and explained you can have (i) anonymous array (ii) extension method (iii)lambda and closure all in a single line.I got spot offer. But..... The interviewer asked me how will you convert an anonymous type into know type :( I am 100% sure ,we can not do that.The interviewer replied there is 200% chance to do that if you have a small work around.I was clueless. As usual,I am waiting for your valuable reply(Is it possible?).

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• django internationalization and translations problem

  - by Zayatzz

  I have a problem with django translations. Problem 1 - i updated string in django.po file, but the change does not appear on the webpage. Problem 2 - i have created my own locale file with django-admin.py makemessages -l et, added the translation string into file, but they too do not appear on the page. I do not think this is setting problem, because the translations from django.po file do appear on the website, its just the changes and the translations from my own generated file that do not appear. Edit: My settings.py contains this: gettext = lambda s: s LANGUAGE_CODE = 'et' LANGUAGES = ( ('et', gettext('Estonian')), ) my own locale files are in /path/to/project/locale/et/LC_MESSAGES/ and the files are django.mo and django.po the file i refer to in problem 1 is django own et transaltion, which i changed.

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• Fast iterating over first n items of an iterable in python

  - by martinthenext

  Hello! I'm looking for a pythonic way of iterating over first n items of a list, and it's quite important to do this as fast as possible. This is how I do it now: count = 0 for item in iterable: do_somethin(item) count += 1 if count >= n: break Doesn't seem neat to me. Another way of doing this is: for item in itertools.islice(iterable, n): do_something(item) This looks good, the question is it fast enough to use with some generator(s)? For example: pair_generator = lambda iterable: itertools.izip(*[iter(iterable)]*2) for item in itertools.islice(pair_generator(iterable), n): so_something(item) Will it run fast enough as compared to the first method? Is there some easier way to do it?

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• Emacs shell output buffer height

  - by jimbo

  Hi , i have the following in my .emacs file(thanks to a SOer nikwin), which evaluates the current buffer content and displays the output in another buffer. (defun shell-compile () (interactive) (save-buffer) (shell-command (concat "python " (buffer-file-name)))) (add-hook 'python-mode-hook (lambda () (local-set-key (kbd "\C-c\C-c") 'shell-compile))) The problem is that the output window takes half the emacs screen. Is there any way to set the output windows's height to something smaller. I googled for 30mins or so and could not find anything that worked. Thanks in advance.

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• Check if the integer in a list is not duplicated, and sequential

  - by prosseek

  testGroupList is a list of integer. I need to check the numbers in testGroupList is sequential (i.e, 1-2-3-4...) and not duplicate numbers. Ignore the negative integer. I implemented it as follows, and it's pretty ugly. Is there any clever way to do this? buff = filter(lambda x: x 0, testGroupList) maxval = max(buff) for i in range(maxval): id = i+1 val = buff.count(id) if val == 1: print id, elif val = 2: print "(Test Group %d duplicated %d times)" % (id, val), elif val == 0: print "(Test Group %d missing)" % id,

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