Tokenizing a string in Prolog using DCG

Let's say I want to tokenize a string of words (symbols) and numbers separated by whitespaces. For example, the expected result of tokenizing "aa 11" would be [tkSym("aa"), tkNum(11)].

My first attempt was the code below:

whitespace --> [Ws], { code_type(Ws, space) }, whitespace.
whitespace --> [].

letter(Let)     --> [Let], { code_type(Let, alpha) }.
symbol([Sym|T]) --> letter(Sym), symbol(T).
symbol([Sym])   --> letter(Sym).

digit(Dg)        --> [Dg], { code_type(Dg, digit) }.
digits([Dg|Dgs]) --> digit(Dg), digits(Dgs).
digits([Dg])     --> digit(Dg).

token(tkSym(Token)) --> symbol(Token). 
token(tkNum(Token)) --> digits(Digits), { number_chars(Token, Digits) }.

tokenize([Token|Tokens]) --> whitespace, token(Token), tokenize(Tokens).
tokenize([]) --> whitespace, [].  

Calling tokenize on "aa bb" leaves me with several possible responses:

 ?- tokenize(X, "aa bb", []).
 X = [tkSym([97|97]), tkSym([98|98])] ;
 X = [tkSym([97|97]), tkSym(98), tkSym(98)] ;
 X = [tkSym(97), tkSym(97), tkSym([98|98])] ;
 X = [tkSym(97), tkSym(97), tkSym(98), tkSym(98)] ;
 false.

In this case, however, it seems appropriate to expect only one correct answer. Here's another, more deterministic approach:

whitespace --> [Space], { char_type(Space, space) }, whitespace.
whitespace --> [].

symbol([Sym|T]) --> letter(Sym), !, symbol(T).
symbol([])      --> [].
letter(Let)     --> [Let], { code_type(Let, alpha) }.

% similarly for numbers

token(tkSym(Token)) --> symbol(Token).

tokenize([Token|Tokens]) --> whitespace, token(Token), !, tokenize(Tokens).
tokenize([]) --> whiteSpace, [].

But there is a problem: although the single answer to token called on "aa" is now a nice list, the tokenize predicate ends up in an infinite recursion:

 ?- token(X, "aa", []).
 X = tkSym([97, 97]).

 ?- tokenize(X, "aa", []).
 ERROR: Out of global stack

What am I missing? How is the problem usually solved in Prolog?

via Chebli Mohamed

Find all numbers in a list integer that add up to a number

I was asked this question on an interview. Given the following list:

[1,2,5,7,10,13]

Find the numbers that add up to 5.

My solution was the following:

#sort the list:
l.sort()
result = ()
for i in range(len(l)):
    for j in range(i, len(l)):
         if l[i] + l[j] > 5:
             break
         elif l[i] + l[j] == 5:
             result += (l[i], l[j])

The idea I presented was to sort the list, then loop and see if the sum is greater than 5. If so, then I can stop the loop. I got the sense the interviewer was dissatisfied with this answer. Can someone suggest a better one for my future reference?

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Woocommerce Show default variation price

I'm using Woocommerce and product variations and all my variations have a default variation defined. I would like to know, how I can find the default variation and display it's price.

This is the code I got so far, but it displays the cheapest variation price, and I'm looking for my default variation product price instead.

// Use WC 2.0 variable price format, now include sale price strikeout
add_filter( 'woocommerce_variable_sale_price_html', 'wc_wc20_variation_price_format', 10, 2 );
add_filter( 'woocommerce_variable_price_html', 'wc_wc20_variation_price_format', 10, 2 );
function wc_wc20_variation_price_format( $price, $product ) {
// Main Price
$prices = array( $product->get_variation_price( 'min', true ), $product->get_variation_price( 'max', true ) );
$price = $prices[0] !== $prices[1] ? sprintf( __( 'HERE YOUR LANGUAGE: %1$s', 'woocommerce' ), wc_price( $prices[0] ) ) : wc_price( $prices[0] );
// Sale Price
$prices = array( $product->get_variation_regular_price( 'min', true ), $product->get_variation_regular_price( 'max', true ) );
sort( $prices );
$saleprice = $prices[0] !== $prices[1] ? sprintf( __( 'HERE YOUR LANGUAGE: %1$s', 'woocommerce' ), wc_price( $prices[0] ) ) : wc_price( $prices[0] );

if ( $price !== $saleprice ) {
    $price = '<del>' . $saleprice . '</del> <ins>' . $price . '</ins>';
}
return $price;

}

I found the code example here Woocommerce variation product price to show default

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Powershell parsing regex in text file

I have a text file:

Text.txt

2015-08-31 05:55:54,881 INFO   (ClientThread.java:173) - Login successful for user = Test, client = 123.456.789.100:12345
2015-08-31 05:56:51,354 INFO   (ClientThread.java:325) - Closing connection 123.456.789.100:12345

I would like output to be:

2015-08-31 05:55:54 Login user = Test, client = 123.456.789.100
2015-08-31 05:56:51 Closing connection 123.456.789.100

Code:

$files = Get-Content "Text.txt"
$grep = $files | Select-String "serviceClient:" , "Unregistered" |  
Where {$_ -match '^(\S+)+\s+([^,]+).*?-\s+(\w+).*?(\S+)$' } |
Foreach {"$($matches[1..4])"} | Write-Host

How can I do it with the current code?

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How to preprocess high cardinality categorical features?

I have a data file which has features of different mobile devices. One column with categorical data type has 1421 distinct types of values. I am trying to train a logistic regression model along with other data that I have. My question is: Will the high cardinality column described above affect the model I am training? If yes, how do I go about preprocessing this column so that it has lower number of distinct values?

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Meteor cursor counts and forEach

I need to add min and max fields into collection items in publish function and filter items by this fileds. I found the solution by using forEach for cursor:

Meteor.publish 'productsWithMinMax', (filter, options) ->
    Products.find(filter, options).forEach (p) =>
        p.min = Math.min p.price1, p.price2, p.price3, p.price4
        p.max = Math.max p.price1, p.price2, p.price3, p.price4

        if p.min && p.max && (p.max < p.mainPrice || p.min > p.mainPrice )
            @added "products", p._id, p

    Counts.publish @, 'numberOfProductsWithMinMax', Products.find(filter), {noReady: true}

    @ready()

But now Counts.publish returns wrong count for my cursor. How to count my cursor in this case?

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ES6 Import Folder

Does the ES6 module syntax allow you to import something from a folder?

For example if I have ./sub/main.js and I try import foo from './sub in the ./main.js file, will this work?

Could I get this sort of importing from a folder to work with babel and webpack?

Basically this would be the equivalent of __init__.py in Python.

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