Extract list of attributes from list of objects in python
attrs = [o.attr for o in objs] was the right code for making a list like the one you describe. Don’t try to subclass list for this. Is there something you did not like about that snippet?
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Difference between a Seq and a List in Scala
In Java terms, Scala’s Seq would be Java’s List, and Scala’s List would be Java’s LinkedList. Note that Seq is a trait, which is similar to Java’s interface, but with the equivalent of up-and-coming defender methods. Scala’s List is an abstract class that is extended by Nil and ::, which are the concrete implementations of … Read more
How to extend a Scala list to enable slicing not by explicit position but by given predicate/condition
List already has a slice method – it takes a subset of elements between a start and end index. What you’re looking for is repeated application of the span method: def span(p: (A) ⇒ Boolean): (List[A], List[A]) Which is documented as: Splits this list into a prefix/suffix pair according to a predicate. Note: c span … Read more
Need to partition a list into lists based on breaks in ascending order of elements (Haskell)
You can do this by resorting to manual recursion, but I like to believe Haskell is a more evolved language. Let’s see if we can develop a solution that uses existing recursion strategies. First some preliminaries. {-# LANGUAGE NoMonomorphismRestriction #-} — because who wants to write type signatures, amirite? import Data.List.Split — from package split … Read more
Using Haskell’s map function to calculate the sum of a list
You can’t really use map to sum up a list, because map treats each list element independently from the others. You can use map for example to increment each value in a list like in map (+1) [1,2,3,4] — gives [2,3,4,5] Another way to implement your addm would be to use foldl: addm’ = foldl … Read more
Python: create a pandas data frame from a list
DataFrame.from_records treats string as a character list. so it needs as many columns as length of string. You could simply use the DataFrame constructor. In [3]: pd.DataFrame(q_list, columns=[‘q_data’]) Out[3]: q_data 0 112354401 1 116115526 2 114909312 3 122425491 4 131957025 5 111373473
How to recursively reverse a list using only basic operations?
(note: the answer is at the bottom of this post) The 2nd function, (define (swap-ends x) ; swap [] = [] (if (or (equal (length x) 0) (equal (length x) 1)) ; swap [x] = [x] x ; swap (x:xs) (cons (first (swap-ends (rest x))) ; | (a:b) <- swap xs (swap-ends (cons (first x) … Read more
Intersection and union of 2 lists
Also, not sure why you’re dead against cuts, so long as their removal would not change the declaritive meaning of the code, as per your link. For example: inter([], _, []). inter([H1|T1], L2, [H1|Res]) :- member(H1, L2), inter(T1, L2, Res). inter([_|T1], L2, Res) :- inter(T1, L2, Res). test(X):- inter([1,3,5,2,4], [6,1,2], X), !. test(X). X = … Read more
“bad words” filter [closed]
Beware of clbuttic mistakes. “Apple made the clbuttic mistake of forcing out their visionary – I mean, look at what NeXT has been up to!” Hmm. “clbuttic”. Google “clbuttic” – thousands of hits! There’s someone who call his car ‘clbuttic’. There are “Clbuttic Steam Engine” message boards. Webster’s dictionary – no help. Hmm. What can … Read more
How to count number of element occurrences in a list in Prolog
The following is based on my previous answer to “Remove duplicates in list (Prolog)” and on this previous answer to the question “Prolog union for A U B U C“. list_item_subtracted_count0_count/5 is derived from list_item_subtracted/3. list_counts/2 is derived from list_setB/2, which were both defined here. list_item_subtracted_count0_count([], _, [], N,N). list_item_subtracted_count0_count([A|As], E, Bs1, N0,N) :- if_(A … Read more