I have local copies of numerous downloaded web-pages. The pages almost certainly have only a few different types of table layouts, but before looking to extract data, I first want to print out the depth and count of the tables that exist on each page.
Using HTML::TableExtract->new( depth => $d, count => $c ) I can iterate over a reasonable range of $d and $c until I get nothing ... a method that works but looks so obviously bad that I'm sure there is a much better way. Please, should I be using a different module than HTML::TableExtract, or is there something more sensible that I should be doing with TableExtract?
Such are the problems of being an infrequent user of Perl but being sure that it's the right tool for a particular job!
I have discovered that my question grew out of my complete misunderstanding of how to use the count and depth arguments in HTML::TableExtract->new() . All the examples I had seen used either the headers=> argument, or else a combination of depth=> and count=>. In fact, neither argument is necessary. What I really needed was to use
$te = HTML::TableExtract->new();
without any arguments to the new() method, and then to use $te->tables_report() to give me exactly the kind of list that I was looking for.
No wonder I didn't get any answers!
Related
I'm relatively new to Ruby, so this is a pretty general question. I have found through the Ruby Docs page a lot of methods that seem to do the exact same thing or very similar. For example chars vs split(' ') and each vs map vs collect. Sometimes there are small differences and other times I see no difference at all.
My question here is how do I know which is best practice, or is it just personal preference? I'm sure this varies from instance to instance, so if I can learn some of the more important ones to be cognizant of I would really appreciate that because I would like to develop good habits early.
I am a bit confused by your specific examples:
map and collect are aliases. They don't "do the exact same thing", they are the exact same thing. They are just two names for the same method. You can use whatever name you wish, or what reads best in context, or what your team has decided as a Coding Standard. The Community seems to have settled on map.
each and map/collect are completely different, there is no similarity there, apart from the general fact that they both operate on collections. map transform a collection by mapping every element to a new element using a transformation operation. It returns a new collection (an Array, actually) with the transformed elements. each performs a side-effect for every element of the collection. Since it is only used for its side-effect, the return value is irrelevant (it might just as well return nil like Kernel#puts does, in languages like C, C++, Java, C♯, it would return void), but it is specified to always return its receiver.
split splits a String into an Array of Strings based on a delimiter that can be either a Regexp (in which case you can also influence whether or not the delimiter itself gets captured in the output or ignored) or a String, or nil (in which case the global default separator gets used). chars returns an Array with the individual characters (represented as Strings of length 1, since Ruby doesn't have an specific Character type). chars belongs together in a family with bytes and codepoints which do the same thing for bytes and codepoints, respectively. split can only be used as a replacement for one of the methods in this family (chars) and split is much more general than that.
So, in the examples you gave, there really isn't much similarity at all, and I cannot imagine any situation where it would be unclear which one to choose.
In general, you have a problem and you look for the method (or combination of methods) that solve it. You don't look at a bunch of methods and look for the problem they solve.
There'll typically be only one method that fits a specific problem. Larger problems can be broken down into different subproblems in different ways, so it is indeed possible that you may end up with different combinations of methods to solve the same larger problem, but for each individual subproblem, there will generally be only one applicable method.
When documentation states that 2 methods do the same, it's just matter of preference. To learn the details, you should always start with Ruby API documentation
I am looking to write a basic profanity filter in a Rails based application. This will use a simply search and replace mechanism whenever the appropriate attribute gets submitted by a user. My question is, for those who have written these before, is there a CSV file or some database out there where a list of profanity words can be imported into my database? We are submitting the words that we will replace the profanities with on our own. We more or less need a database of profanities, racial slurs and anything that's not exactly rated PG-13 to get triggered.
As the Tin Man suggested, this problem is difficult, but it isn't impossible. I've built a commercial profanity filter named CleanSpeak that handles everything mentioned above (leet speak, phonetics, language rules, whitelisting, etc). CleanSpeak is capable of filtering 20,000 messages per second on a low end server, so it is possible to build something that works well and performs well. I will mention that CleanSpeak is the result of about 3 years of on-going development though.
There are a few things I tell everyone that is looking to try and tackle a language filter.
Don't use regular expressions unless you have a small list and don't mind a lot of things getting through. Regular expressions are relatively slow overall and hard to manage.
Determine if you want to handle conjugations, inflections and other language rules. These often add a considerable amount of time to the project.
Decide what type of performance you need and whether or not you can make multiple passes on the String. The more passes you make the slow your filter will be.
Understand the scunthrope and clbuttic problems and determine how you will handle these. This usually requires some form of language intelligence and whitelisting.
Realize that whitespace has a different meaning now. You can't use it as a word delimiter any more (b e c a u s e of this)
Be careful with your handling of punctuation because it can be used to get around the filter (l.i.k.e th---is)
Understand how people use ascii art and unicode to replace characters (/ = v - those are slashes). There are a lot of unicode characters that look like English characters and you will want to handle those appropriately.
Understand that people make up new profanity all the time by smashing words together (likethis) and figure out if you want to handle that.
You can search around StackOverflow for my comments on other threads as I might have more information on those threads that I've forgotten here.
Here's one you could use: Offensive/Profane Word List from CMU site
Based on personal experience, you do understand that it's an exercise in futility?
If someone wants to inject profanity, there's a slew of words that are innocent in one context, and profane in another so you'll have to write a context parser to avoid black-listing clean words. A quick glance at CMU's list shows words I'd never consider rude/crude/socially unacceptable. You'll see there are many words that could be proper names or nouns, countries, terms of endearment, etc. And, there are myriads of ways to throw your algorithm off using L33T speak and such. Search Wikipedia and the internets and you can build tables of variations of letters.
Look at CMU's list and imagine how long the list would be if, in addition to the correct letter, every a could also be 4, o could be 0 or p, e could be 3, s could be 5. And, that's a very, very, short example.
I was asked to do a similar task and wrote code to generate L33T variations of the words, and generated a hit-list of words based on several profanity/offensive lists available on the internet. After running the generator, and being a little over 1/4 of the way through the file, I had over one million entries in my DB. I pulled the plug on the project at that point, because the time spent searching, even using Perl's Regex::Assemble, was going to be ridiculous, especially since it'd still be so easy to fool.
I recommend you have a long talk with whoever requested that, and ask if they understand the programming issues involved, and low-likelihood of accuracy and success, especially over the long-term, or the possible customer backlash when they realize you're censoring them.
I have one that I've added to (obfuscated a bit) but here it is: https://github.com/rdp/sensible-cinema/blob/master/lib/subtitle_profanity_finder.rb
Are there any downsides to passing in an Erlang record as a function argument?
There is no downside, unless the caller function and the called function were compiled with different 'versions' of the record.
Some functions from erlangs standard library do indeed use records in their interfaces (I can't recall which ones, right now--but there are a few), but in my humble opinion, the major turnoff is, that the user will have to include your header file, just to use your function.
That seems un-erlangy to me (you don't ever do that normally, unless you're using said functions from the stdlib), creates weird inter-dependencies, and is harder to use from the shell (I wouldn't know from the top of my head how to load & use records from the shell -- I usually just "cheat" by constructing the tuple manually...)
Also, handling records is a bit different from the stuff you usually do, since their keys per default take the atom 'undefined' as value, au contraire to how you usually do it with proplists, for instance (a value that wasn't set just isn't there) -- this might cause some confusion for people who do not normally work a lot with records.
So, all-in-all, I'd usually prefer a proplist or something similar, unless I have a very good reason to use a record. I do usually use records, though, for internal state of for example a gen_server or a gen_fsm; It's somewhat easier to update that way.
I think the biggest downside is that it's not idiomatic. Have you ever seen an API that required you to construct a record and pass it in?
Why would you want to do something that's going to feel foreign to any erlang programmer? There's a convention already in use for optional named arguments to functions. Inventing yet another way without good cause is pointless.
Seems like it's inconsistent in the lists module. For example, split has the number as the first argument and the list as the second, but sublists has the list as the first argument and the len as the second argument.
OK, a little history as I remember it and some principles behind my style.
As Christian has said the libraries evolved and tended to get the argument order and feel from the impulses we were getting just then. So for example the reason why element/setelement have the argument order they do is because it matches the arg/3 predicate in Prolog; logical then but not now. Often we would have the thing being worked on first, but unfortunately not always. This is often a good choice as it allows "optional" arguments to be conveniently added to the end; for example string:substr/2/3. Functions with the thing as the last argument were often influenced by functional languages with currying, for example Haskell, where it is very easy to use currying and partial evaluation to build specific functions which can then be applied to the thing. This is very noticeable in the higher order functions in lists.
The only influence we didn't have was from the OO world. :-)
Usually we at least managed to be consistent within a module, but not always. See lists again. We did try to have some consistency, so the argument order in the higher order functions in dict/sets match those of the corresponding functions in lists.
The problem was also aggravated by the fact that we, especially me, had a rather cavalier attitude to libraries. I just did not see them as a selling point for the language, so I wasn't that worried about it. "If you want a library which does something then you just write it" was my motto. This meant that my libraries were structured, just not always with the same structure. :-) That was how many of the initial libraries came about.
This, of course, creates unnecessary confusion and breaks the law of least astonishment, but we have not been able to do anything about it. Any suggestions of revising the modules have always been met with a resounding "no".
My own personal style is a usually structured, though I don't know if it conforms to any written guidelines or standards.
I generally have the thing or things I am working on as the first arguments, or at least very close to the beginning; the order depends on what feels best. If there is a global state which is chained through the whole module, which there usually is, it is placed as the last argument and given a very descriptive name like St0, St1, ... (I belong to the church of short variable names). Arguments which are chained through functions (both input and output) I try to keep the same argument order as return order. This makes it much easier to see the structure of the code. Apart from that I try to group together arguments which belong together. Also, where possible, I try to preserve the same argument order throughout a whole module.
None of this is very revolutionary, but I find if you keep a consistent style then it is one less thing to worry about and it makes your code feel better and generally be more readable. Also I will actually rewrite code if the argument order feels wrong.
A small example which may help:
fubar({f,A0,B0}, Arg2, Ch0, Arg4, St0) ->
{A1,Ch1,St1} = foo(A0, Arg2, Ch0, St0),
{B1,Ch2,St2} = bar(B0, Arg4, Ch1, St1),
Res = baz(A1, B1),
{Res,Ch2,St2}.
Here Ch is a local chained through variable while St is a more global state. Check out the code on github for LFE, especially the compiler, if you want a longer example.
This became much longer than it should have been, sorry.
P.S. I used the word thing instead of object to avoid confusion about what I was talking.
No, there is no consistently-used idiom in the sense that you mean.
However, there are some useful relevant hints that apply especially when you're going to be making deeply recursive calls. For instance, keeping whichever arguments will remain unchanged during tail calls in the same order/position in the argument list allows the virtual machine to make some very nice optimizations.
I've got a massive script with about 20 embedded if statements (Yay!) that is used to parse through a data file. And in a sense, that's correct because the script should not continue operating if any of those evaluations fail.
But my gut says there's a more elegant way to accomplish the same thing. I'm familiar with the statemachine plugin for rails, but that seems to be overkill (it seems to be overkill).
Any chance there's a slightly more elegant way to reduce the number of embedded 'ifs' either through a workflow, or some other way?
reverse the conditions of the if statements and leave the particular function(if you can). This way you get a lot of if's behind each other instead of nested
This is mostly code specific, but I can suggest 2 ways:
case .. when .. then .. structure.
Effectively using send or eval methods.
One approach is to construct a hash or array in which the contents are Procs that each encapsulate a given conditional. Then you can loop through the procs and test your data against each one.
Just refactor the code and split parts of the conditional sections out to different functions. It will not reduce the nested if deepths but make it more readable.
Otherwise there is very little to say as it is a very generic question.
Use haml :P
(so you dont need to end the if tags..)