I'm trying to solve a problem statement using C# as programming language.
In the problem system for an input (double/decimal) say Hi, the output generated is a form of dataset containing number of parameters (Fi, Pi and Ti). I somehow have to filter out only those entries in the data set which would satisfy the following conditions.
Fi > Fmin, where Fmin is some constant
Pi > Pmin, where Pmin is some constant
Ti < Tmax, where Tmax is some constant
Is there an efficient algorithm I could use in such cases where I could zero in on an optimal set of values for Hi for which the output parameter values are well within the constraints. Also I thought using Genetic Algorithms in this case makes sense but somehow I'm not able to formulate and fit the problem specific to Genetic Algorithms.
Any pointers/ suggestions are truly appreciated.
you can use Linq query
var result = DataSet.Where(x=>x.Fi> Fmin && x.Pi>Pmin && Ti < Tmax);
Well, it's hard for me to guess. I don't know the properties of the function for Fi etc.
An log-Barrier Method could be something interesting here. Or the SQP Method. But it has to be differntiable.
Otherwise simulated annealing could be interesting.
But these are just some guesses. It really depends on the problem.
I doubt that a Genetic Algorithm makes sense, seeing as you have only one input variable (Hi) that determines the outputs (Fi, Pi, Ti). The power of a Genetic Algorithm is that it blends good solutions into new solutions. If your solution is only one number, blending two good solutions will probably mean that you're finding some Hi inbetween (such as the average -> 0.5Hi1 + 0.5Hi2 or some other linear combination aHi1 + (1-a)Hi2 with a between 0 and 1).
I would recommend looking into Multi-start Local Search heuristics, such as link. This is a pretty solid heuristic that allows you to explore the solution space for Hi.
In their simplest form, such heuristics calculate the performance for N random values of Hi, and then search for further improvements in the area of the best performing Hi values out of those N initial values.
This sort of stuff is also pretty straight-forward to code, assuming that you have a way to obtain the Fi, Ti, and Pi values from your Hi input, and that you have some way to figure out which of your solutions perform 'best' (for instance through a fitness function as mentioned in the comments).
I learned basic algorithms on visual C# in highschool, and I made a simple code that numerically integrates a math function within given limits.
I want to be able to change the function the code integrates without actually editing the code, so I googled it for a while and found a lot of articles about how to do it. I tired to understand it but the problem is I can't understand any of what's written there because it's too much above my level.
I need a code that can add code on the run from a string containing a math function, that can accept a variable, log, ln, powers, sin, cos, tan and maybe pi and e, that is ready in a friendly "copy-paste" format, followed by instructions on where to paste it, and how to connect it to my code. To clarify:
I want to take something like this:
string s = "Sqrt(ln(1 + x ^ 2))";
and make it like this:
double x = 0;
double y = Math.Sqrt(Math.Log(1 + Math.Pow(x,2)));
I know it's a pretty annoying request and if it's not the right place to ask such a thing I apologize in advance.
This is actually fairly difficult to do in a language like C#, as it's statically compiled.
A good alternative would be to use an expression parsing library, such as NCalc. This library would allow you to create the expression (your string), parse it, and extract the result.
I need to enable user that he can write own formula in datagridview. Something like a function in Excel.
Example of formula definition:
So, user write his own formula in formula cell and then in other table is shown result for each. How I can do this?
I would try NCalc
NCalc is a mathematical expressions evaluator in .NET. NCalc can parse any expression and evaluate the result, including static or dynamic parameters and custom functions.
Dictionary<string, int> dict = new Dictionary<string, int>() { { "Income", 1000 }, { "Tax", 5 } };
string expressionString = "Income * Tax";
NCalc.Expression expr = new NCalc.Expression(expressionString);
expr.EvaluateParameter += (name, args) =>
{
args.Result = dict[name];
};
int result = (int)expr.Evaluate();
Your formula could be manipulated to C# and dynamically compiled using SystemCodeCom.Compiler and you could run it on the fly feeding in your variable values.
Otherwise you are going to have to impliment some kind of mini parser/compiler - which is a rather particular skill and which could quickly get complicated - especially if your formulas become more complicated (which maybe likely).
There is are codeproject articles on dynamic complilation here and here. But there are plenty of other examples around on the web.
There are a number of ways you can do that, they all revolve around translating the formula into executable code.
Do you want to write your own parser or do you wnat to use an existing one. C# itself, IronPython, IronRuby, some off the shelf component. If you use a full parser you might want to look at how to restrict what the user can do with it, inadvertantly or otherwise...
If they are as simple as they look, some sort of expression builder, (pick two named values and an operator) might be the way to go, but modularise, both building the expression and evaluating it so you can beef up at some later point.
However given how simple they appear to be, I'd be tempted to predefine expressions (loaded as meta data from some sort of backing store, and make it select one of these as opposed to user entering it. You could easily spend months at this aspect of the design, is it worth it?
I had a similar requirement (dynamic parsing of expressions) recently in a project I am working on and ended up using VB expressions from WF (Windows Workflow Foundation). It certainly depends on how important this functionality is for you and how much effort are you willing to put into it. In my case it turned out better than NCalc for several reasons:
it supports more complex expressions than NCalc
the resulting expression trees can be analyzed to determine dependencies for individual expressions
it's the same language for expressions as in WF (which I already use elsewhere in the project)
Anyway, here is a short blogpost I've written on the subject.
I created the albatross expression parser a few years back. It has been open sourced for a while but I finally get around and published v2.02 and added documentation recently. It is being actively maintained. It has a couple nice features:
Circular reference detection
Source variable from external object directly
Reversed generation of expressions
Properly documented
I'm in need to estimate localization effort needed for a legacy project. I'm looking for a tool that I could point at a directory, and it would:
Parse all *.cs files in the directory structure
Extract all C# string literals from the code
Count total number of occurrences of the strings
Do you know any tool that could do that? Writing it would be simple, but if some time can be saved, then why not save it?
Use ILDASM to decompile your .DLL / .EXE.
I just use options to dump all, and you get an .il file with a section "User String":
User Strings
-------------------------------------------------------
70000001 : (14) L"Starting up..."
7000001f : (12) L"progressBar1"
70000039 : (21) L"$this.BackgroundImage"
70000065 : (10) L"$this.Icon"
7000007b : ( 6) L"Splash"
Now if you want to know how many time a certain string is used. Search for a "ldstr" like this:
IL_003c: /* 72 | (70)000001 */ ldstr "Starting up..." /* 70000001 */
I think this will be a lot easier to parse as C#.
Doing a quick search, I found the following tool that may or may not be useful to you.
http://www.devincook.com/goldparser/
I also found another SO user who was trying to do something similar.
Regex to parse C# source code to find all strings
Well, if you have hardcoded strings, you need to know what is your i18n effort first (unhardcoding them could be quite painful). Another issue: you need to count translatable words not distinct strings, that is the input for translation providers. And even though string might seem duplicated, it could be translated in a different way depending on the context, so you don't need to care about "distninct", you just have to count all words... That's how Localization works per my experience.
In most common development, you should keep your strings external to your program source code. In your case, could you spare the effort to extract the strings into a resource file?
If so, then you can make use of the default localization solution in .NET, i.e.
resource.resx,
resource.fr.resx,
resources.es.resx
stores strings for different locales.
Updated :
The actual implementation depends on your project architecture/technology, resource files ain't the best way to do this, but it is the easiest, and the recommended way in .NET.
Like in this article
A few more tutorials
A few more tutorials
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I've mainly been doing C# development for the past few years but recently started to do a bit of Python (not Iron Python). But I'm not sure if I've made the mental leap to Python...I kind of feel I'm trying to do things as I would in C#.
Any advice on how I can fully take advantage of Python?
Or any tips\tricks, things to learn more about, things to watch out for?
First, check tgray's and Lundström's advice.
Then, some things you may want to know:
Python is dynamically typed, so unlike C#, you will not
check type, but behavior. You may want to google about duck
typing. It implies you do not have to deal with boxing and
unboxing.
Python is fully object oriented, but the syntax does not
enforce this paradigm. You can write Python without using
the word "class".
The GUI library featured with Python can't compare with
C#'s. Check PyQt, GTK or wxPython libraries.
Python has a lot of concepts you may not be familiar with:
list comprehensions, generators ("yield" does exist in C#,
but it is not used much), decorators, metaclasses, etc. Don't
be afraid; you can program in Python without them. They
are just smart tools, not mandatory.
Like in C#, the Python standard library is huge. Always
look at it when you encounter any problem. It is most
likely that someone solved it already.
Python use LATE binding and variable labels. It's far too
early for somebody starting with the language to worry
about it, but remember that one day you will encounter a
behavior with variables that SEEMS illogical, and you'll
have to check that. For the moment:
Just remember to never do the following:
def myfunc(my_list=[]) :
# bla
Instead:
def myfunc(my_list=()) :
my_list = list(my_list)
And you'll be good. There is a good reason for that, but
that's not the point :-)
Python is cross platform, enjoy writing on Mac, and
run on Linux, if you wish.
Python is not provided with a complex IDE (you got IDLE :-)).
If you are a Visual Studio addict, check Glade. This is
not as advanced as Visual Studio, but it's still a good RAD.
If you want to develop some web application in Python,
remember that Python is not .NET. You must add a web
framework to it if you want to compare. I like Django.
Python does not need a huge IDE to work with. SciTE,
Notepad++, IDLE, Kate, gedit...
Lightweight editors are really sufficient.
Python enforces indentation using spaces and line break,
you can't change that. You should avoid using tabs for
indenting and choose spaces instead. The equivalent of
empty bracelets {} is the keyword "pass".
Python does not enforce private variables. You can define a
private var using "__" (two underscores) at the beginning of
the variable name, but it's still bypassable in some tricky
ways. Python usually assume programmers are grown adults
that know what they do and communicate.
Python uses iteration. A lot. A lot of a lot. And so the
itertools module is you best friend.
Python has no built in delegates. The delegate module is
not what you think. For event-driven programming, use a
GUI lib (or code the pattern yourself, it's not that
difficult).
Python has an interpreter: you can test almost anything,
live. It should always be running next to your text
editor. Python basic interpreter is not much, try IPython
for something tasty.
Python is autodocumented: use docstrings in your own code
and consult other's using "help()" in the python interpreter
Module basics:
sys: manipulate system features
os: set credential, manipulate file paths, rename, recursive file walk, etc
shutil: batch file processing (such as recursive delete)
re: regexp
urllib and urllib2: HTTP¨scripting like downloading, post / get resquests, etc.
datetime: manipulate date, time AND DURATION
thread: you guess it
zlib: compression
pickle: serialization
xml: parsing / Writing XML with SAX or DOM
There are hundreds of modules. Enjoy.
Some typical ways to do things in Python:
Loops:
Python coders use massively the equivalent of the foreach C#
loop, and prefer it to any others:
Basic iterations:
for item in collection:
print str(item)
"collection" can be a string, a list, a tuple... Any
iterable: any object defining the .next() method. There are
a lot of iterables in Python. E.g: a typical Python idiom
to read files:
for line in open("/path/to/file") :
print line
A shortcut to the for loop is called "list comprehension".
It's a way to create an new iterable in one line:
Creating a filtered list with list comprehension:
my_list = [item for item in collection if condition]
Creating a new list with a list comprehension:
my_list = [int(item) * 3 for item in collection]
Creating a new generator with a list comprehension:
my_list = (int(item) * 3 for item in collection)
Same as above, but the values will be generated on the fly
at the first iteration then lost. More information about it here.
Ordinary for loop
If you want to express a usual for loop, you can use the
xrange() function. for (int i = 0; i < 5; i++) becomes:
for i in xrange(0,5) :
do while equivalent
There is no "Do While" in Python. I never missed it, but if
you have to use this logic, do the following:
while True : # Yes, this is an infinite loop. Crazy, hu?
# Do your stuff
if condition :
break
Unpacking
Swapping variables:
a, b = b, a
Multiple assignations:
The above is just a result of what we call "unpacking" (here
applied to a tuple). A simple way to explain it is that you
can assign each value of any sequence directly to an equal
number a variables, in one row:
animal1, animal2, animal3, animal4 = ["cow", "dog", "bird", "fish"]
This has a lot of implications. While iterating on a
multidimensional array, you normally get each sub sequence
one by one then use it, for example:
agenda = [("steve", "jobs"), ("linus", "torvald"), ("bill", "gates"),("jon", "skeet")]
for person in agenda:
print person[0], person[1]
But with unpacking, you can assign the values directly to
variables as well:
agenda = [("steve", "jobs"), ("linus", "torvald"), ("bill", "gates"),("jon", "skeet")]
for name, lastname in agenda:
print name, lastname
And that's why if you want to get an index while iterating,
Python coders use the following idioms (enumerate() is a
standard function):
for index, value in enumerate(sequence) :
print index, value
Unpacking in functions calls
This is advanced use, and you can skip it if it bothers you.
You can unpack values using the sign "*" to use a sequence
directly in a function call. E.g:
>>> foo(var1, var1, var3) :
print var1, var2
print var3
>>> seq = (3.14, 42, "yeah")
>>> foo(*seq)
3.14 42
yeah
There is even more than that. You can unpack a dictionary as
named variables, and write function prototypes with *,
** to accept an arbitrary number of arguments. But it not
used enough to deserve to make this post even longer :-).
String formatting:
print "This is a %s on %s about %s" % ("post", "stackoverflow", "python")
print "This is a %(subject)s on %(place)s about %(about)s" % {"subject" : "post", "place" : "stackoverflow", "about" : "python"}
Slicing an iterable:
You can get any part of an iterable using a very concise syntax:
print "blebla"[2:4] # Print "eb"
last = string[:-1] # Getting last element
even = (0,1,2,3,4,5,6,7,8,9)[::2] # Getting evens only (third argument is a step)
reversed = string[::-1] # Reversing a string
Logical checks:
You can check the way you do in C#, but there are "Pythonic"
ways (shorter, clearer :-)):
if 1 in (1, 2, 3, 4) : # Check en element is in a sequence
if var : # check is var is true. Var == false if it's False, 0, (), [], {} or None
if not var : # Contrary of above
if thing is var: # Check if "thing" and "var" label the same content.
if thing is None : # We use that one because None means nothing in Python (almost null)
Combo (print on one line all the words containing an "o" in uppercase ):
sentence = "It's a good day to write some code"
print " ".join([word.upper() for word in sentence.split() if "o" in word])
Output: "GOOD TO SOME CODE"
Easier to ask for forgiveness than permission
Python coders usually don't check if something is possible. They are a bit like Chuck Norris. They do it. Then catch the exception. Typically, you don't check if a file exists, you try to open it, and roll back if it fails:
try :
f = open(file)
except IOerror :
print "no file here !"
Of course Chuck Norris never uses excepts since he never fails.
The else clause
"Else" is a world of many uses in Python. You will find
"else" after "if", but after "except" and "for" as well.
for stuff in bunch :
# Do things
else :
# This always happens unless you hit "break" in the loop
This works for "while" loop too, even if we do not use this
loop as much.
try :
# A crazy stuff
except ToCrazyError :
# This happens if the crazy stuff raises a ToCrazyError Exception
else :
# This will happen if there is no error so you can put only one line after the "try" clause
finally :
# The same as in C#
If you are curious, here is a bunch of advanced quick and
dirty (but nice) Python snippets.
Refrain from using classes. Use dictionaries, sets, list and tuples.
Setters and getters are forbidden.
Don't have exception handlers unless you really need to - let it crash in style.
Pylint can be your friend for more pythonish coding style.
When you're ready - check out list comprehensions, generators and lambda functions.
If you are not new to programming, I would recommend the book "Dive into Python" by Mark Pilgrim. It explains Python in a way that makes it easy to understand how Python techniques and idioms can be applied to build practical applications.
Start by reading The Zen of Python
You can read it at the link above, or just type import this at the Python prompt. =)
Take advantage of Python features not offered* by C#
Such as duck-typing, metaclasses, list comprehension, etc.*
Write simple programs just to test these features. You'll get used (if not addicted) to them in no time.
Look at the Python Standard Library
So you don't reinvent the wheel. Don't try to read the whole thing, even a quick look at the TOC could save you a lot of time.
* I know C# already has some of these features, but from what I can see they're either pretty new or not commonly used by C# developers. Please correct me if I'm wrong.
In case you haven't heard about it yet, Dive Into Python is a great place to start for anyone learning Python. It also has a bunch of Tips & Tricks.
If you are someone who is better learning a new language by taking small incremental steps then I would recommend using IronPython. Otherwise use regular CPython and don't do any more C# coding until you feel like you have a grasp of Python.
I would suggest getting a good editor so that you don't get bitten by whitespace. For simplicity, I just use ActivePython's packages Link, which include an editor and all of the win32api libraries. They are pretty fun to get into if you have been using C#. The win32api in Python can be a little bit simpler. You don't need to do the whole DDLImport thing. Download ActivePython (which comes with CPython), open it up, and start entering some stuff at the console. You will pick it up fairly easy after using C#. For some more interesting Python tidbits, try ActiveState code, which has all sorts of recipes, which can allow you to very simply see different things that you can do with Python.
I'm pretty much in your shoes too, still using C# for most of my work, but using Python more and more for other projects.
#e-satis probably knows Python inside-out and all his advice is top-notch. From my point of view what made the biggest difference to me was the following:
Get back into functional. not necessarily spaghetti code, but learning that not everything has to be in an object, nor should it be.
The interpreter. It's like the immediate window except 10^10 better. Because of how Python works you don't need all the baggage and crap C# makes you put in before you can run things; you can just whack in a few lines and see how things work.
I've normally got an IDLE instance up where I just throw around snippets as I'm working out how the various bits in the language works while I'm editing my files... e.g. busy working out how to do a map call on a list, but I'm not 100% on the lambda I should use... whack in a few lines into IDLE, see how it works and what it does.
And finally, loving into the verbosity of Python, and I don't mean that in the long winded meaning of verbosity, but as e-satis pointed out, using verbs like "in", "is", "for", etc.
If you did a lot of reflection work in C# you'll feel like crying when you see how simple the same stuff is in Python.
Good luck with it.
If you have programming experience and don't feel like spending money I'd recommend How to Think Like a Computer Scientist in Python.
And then something you can benefit from:
IPython shell: Auto completion in the shell. It does batch operations, adds a ton of features, logging and such. >>> Play with the shell - always!
easy_install / pip: So nice and an easy way to install a 3rd party Python application.