LINQ Ruined My Favorite Interview Question • Hacker News Board

Re: LINQ Ruined My Favorite Interview Question

#41

Post by cavilling_elite » Thu, Jul 11, 2013, 3:13 PM UTC

archangel_one wrote: post #27

untog wrote: post #21

Earlier quoted context omitted.

Well, sure, once you're allowed to use external libraries anything is a one line solution. In JS: doStuff = require("doStuff"); var result = doStuff(theString); isn't JS so efficient ?!?

collections isn't an external library. It's part of the Python standard library.

Agreed, if I was looking for a candidate that will always "reinvent the wheel" then I would want them to implement from scratch. I find it perfectly valid for the interviewee to say "Hey! I wrote a module for for this exact purpose! Want to check out my github page?".

Re: LINQ Ruined My Favorite Interview Question

#42

Post by untog » Thu, Jul 11, 2013, 3:13 PM UTC

jkrems wrote: post #25

untog wrote: post #21

Earlier quoted context omitted.

Well, sure, once you're allowed to use external libraries anything is a one line solution. In JS: doStuff = require("doStuff"); var result = doStuff(theString); isn't JS so efficient ?!?

It looks like collections is part of the standard library: http://docs.python.org/2/library/collections.html . I think this disqualifies your JS solution, as long as doStuff isn't some fancy nodejs core module I missed.

I think the point still stands though, when you think of it as an interview question. The point is to get to the bottom of how the candidate would process such a query themselves, not to test their knowledge of the core libraries of their favourite language. I feel like that's what the post author meant when he said that LINQ had "ruined" the question- because it kind of does the same thing.

Re: LINQ Ruined My Favorite Interview Question

#43

Post by colanderman » Thu, Jul 11, 2013, 3:13 PM UTC

llambda wrote: post #8

I hate to be the bearer of bad news, but I think there may be even simpler solutions to this problem: (take 10 (reverse (sort-by (comp first rest) (frequencies (string/split ... #"\+s")))) The above is a Clojure one-liner example that I believe satisfies the original problem. So while LINQ may have simplified from the C-language family solutions he had seen, it's clearly possible to take it one step further with the…

expressivity of modern languages like Clojure

Uh, no. Your solution just uses a bunch of standard library functions (at least, I hope they're not syntactic forms… and why a function as specific as "frequencies" not in some namespace boggles my mind). I could write that in C with an appropriate standard library.

Ironically, expressing this in something like SQL actually speaks to the expressivity of the language because the solution was produced entirely with syntactic forms.

Re: LINQ Ruined My Favorite Interview Question

#44

Post by aphyr » Thu, Jul 11, 2013, 3:16 PM UTC

llambda wrote: post #8

I hate to be the bearer of bad news, but I think there may be even simpler solutions to this problem: (take 10 (reverse (sort-by (comp first rest) (frequencies (string/split ... #"\+s")))) The above is a Clojure one-liner example that I believe satisfies the original problem. So while LINQ may have simplified from the C-language family solutions he had seen, it's clearly possible to take it one step further with the…

While we're golfing, (comp first rest) is equivalent to the stdlib function called second, or, perhaps more idiomatic for map entries, val. We can also flatten deeply nested chains of computation using the -> and ->> macros, like so:

  (->> (string/split ... #"\s+")
       frequencies
       (sort-by val)
       reverse
       (take 10))

Re: LINQ Ruined My Favorite Interview Question

#45

Post by alevans4 » Thu, Jul 11, 2013, 3:18 PM UTC

untog wrote: post #17

overgard wrote: post #4

LINQ tends to get thought of as "database syntax sugar", but it's way more than that. It's C#'s version of the lazy collection operations you find in most functional languages, just given friendlier sqlish names. (IE, "Select" instead of "map" and "Where" instead of "filter") I almost feel a bit gross when I have to write a "foreach" loop at this point, because there's almost always an equivalent way to do it in LINQ…

I almost feel a bit gross when I have to write a "foreach" loop at this point Agreed. I've transitioned to spending most of my time in JS, and wherever I can I use .map(), but the chaining it's not quite the same as LINQ. Someday I intend to write a library of Array addons to provide GroupBy and so on, but I can't imagine it'll be super efficient.

Underscore has groupBy and some of the others you may be looking for.

Re: LINQ Ruined My Favorite Interview Question

#46

Post by seivan » Thu, Jul 11, 2013, 3:18 PM UTC

I would have used a weighted SET.

But it's funny, the first time I read the paragraph, I'd assume the words were not separated by space, and you had to find occurrences of combinations than.

I instinctively made the test much harder than it would be. I'm damaged.

Re: LINQ Ruined My Favorite Interview Question

#47

Post by GregWright » Thu, Jul 11, 2013, 3:19 PM UTC

mrottenkolber wrote: post #22

llambda wrote: post #8

I hate to be the bearer of bad news, but I think there may be even simpler solutions to this problem: (take 10 (reverse (sort-by (comp first rest) (frequencies (string/split ... #"\+s")))) The above is a Clojure one-liner example that I believe satisfies the original problem. So while LINQ may have simplified from the C-language family solutions he had seen, it's clearly possible to take it one step further with the…

how does FREQUENCIES know how to compare strings? In Common Lisp you'd usually supply a TEST keyword parameter (#'STRING= or #'EQUAL in this case). Does Clojure use Java's type system to infer?

No expert, but from the source it looks like it just uses whatever a 'map' uses to match keys:

  (defn frequencies
    "Returns a map from distinct items in coll to the number of times
    they appear."
    {:added "1.2"
     :static true}
    [coll]
    (persistent!
     (reduce (fn [counts x]
               (assoc! counts x (inc (get counts x 0))))
             (transient {}) coll)))

Re: LINQ Ruined My Favorite Interview Question

#48

Post by untog » Thu, Jul 11, 2013, 3:19 PM UTC

alevans4 wrote: post #45

untog wrote: post #17

Earlier quoted context omitted.

I almost feel a bit gross when I have to write a "foreach" loop at this point Agreed. I've transitioned to spending most of my time in JS, and wherever I can I use .map(), but the chaining it's not quite the same as LINQ. Someday I intend to write a library of Array addons to provide GroupBy and so on, but I can't imagine it'll be super efficient.

Underscore has groupBy and some of the others you may be looking for.

Yes.. I do understand why extending the base Array object in JS is deeply frowned upon but at the same time I often wish that these sort of extensions were on the Array object. It feels clunky to use them otherwise.

Re: LINQ Ruined My Favorite Interview Question

#49

Post by teh_klev » Thu, Jul 11, 2013, 3:20 PM UTC

kryten wrote: post #20

moomin wrote: post #13

I hate to be the arrogant know it all on Hacker News, but seriously, if you're writing c# and not using LINQ all the time, you need to catch up. I'm tired of seeing people answer interview questions with anything _other_ than LINQ.

LINQ is not a magic bullet. It has some serious pitfalls. I'd like to aee people using the right tools for the job.

LINQ is a great mechanism for expressing complex operations in a succinct manner. Sure, LINQ may not be a magic bullet and can be abused, but you know the old adage about premature optimisation. Perhaps you could elaborate on "It has some serious pitfalls.".

Re: LINQ Ruined My Favorite Interview Question

#50

Post by [deleted] » Thu, Jul 11, 2013, 3:21 PM UTC

mrottenkolber wrote: post #22

llambda wrote: post #8

I hate to be the bearer of bad news, but I think there may be even simpler solutions to this problem: (take 10 (reverse (sort-by (comp first rest) (frequencies (string/split ... #"\+s")))) The above is a Clojure one-liner example that I believe satisfies the original problem. So while LINQ may have simplified from the C-language family solutions he had seen, it's clearly possible to take it one step further with the…

how does FREQUENCIES know how to compare strings? In Common Lisp you'd usually supply a TEST keyword parameter (#'STRING= or #'EQUAL in this case). Does Clojure use Java's type system to infer?

[deleted]