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LINQ Ruined My Favorite Interview Question

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Re: LINQ Ruined My Favorite Interview Question

#91

Post by corresation »

Strilanc wrote: post #75
corresation wrote: post #71

Earlier quoted context omitted.

I'm not sure what you're actually arguing for or against. There is nothing at all wrong with functional programming, and such had nothing whatsoever to do with my comment. That LINQ happens to use some functional techniques doesn't make my criticism a criticism of fP.

Functional languages use the concepts you're criticizing even more extensively than LINQ does.

What are the "concepts I'm criticizing"? I suspect that you have absolutely no idea what the context of my comment was, because your diversion on the topic of functional programming is just grossly out of place.

LINQ encourages the belief that set operations are free, such that you no longer have to concern yourself with concepts like memoization or appropriate structures. This has nothing to do with functional programming. Literally at all.

Re: LINQ Ruined My Favorite Interview Question

#92

Post by PaulAJ »

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.

This is the problem with doing functional list stuff in languages that permit side effects: the order of execution for each function has to be strictly defined (in both senses of the word), so the compiler can't optimise the code. In Haskell the solution (see my comment on the original page) would probably (I haven't actually checked the GHC core output) be folded into a single loop.

Re: LINQ Ruined My Favorite Interview Question

#93

Post by shill »

spenuke wrote: post #68
shill wrote: post #31

Earlier quoted context omitted.

Without imports: d = {} for word in s1.split(' '): try: d[word] += 1 except KeyError: d[word] = 1 print [(x, d[x]) for x in sorted(d, key=d.get, reverse=True)][:10]

I'm a newbie, but the question seemed approachable so I went for it. This is what I came up with. (Python, btw.) def top_ten(s): words = s.split(' ') word_list = set(words) return sorted(word_list, key=lambda x: words.count(x))[:10] The question didn't ask for word counts, so I didn't see the need for a dictionary. I'd appreciate any advice on my solution. I'd be thrilled if I'm not too far off from being capable of…

> I'd appreciate any advice on my solution.

You should always compare your results to what is expected. For a problem like this, use a small set of test data that can easily be counted and sorted in your head or on paper.

You forgot reverse=True and your results show the 10 least common words. ;)

This kind of error happens to all of us. That's why we have unit tests and QA teams. If you made this mistake during an interview I wouldn't give it much importance and we would have a good laugh about it.

Re: LINQ Ruined My Favorite Interview Question

#94

Post by JeanPierre »

wging wrote: post #63
aphyr wrote: post #44

Earlier quoted context omitted.

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))

If the aim is golf, it's probably best to keep #" ". If the aim is accuracy, we might get better results by using #"[^\w]+". Though that does nasty things to words like "it's". Edit: Actually, we can also get rid of the 'reverse' by replacing (sort-by val) with (sort-by (comp - val)). Not going to be shorter in terms of character count, though we win on line count.

sort-by takes an optional comparator, so doing (comp - val) is a bit unneeded. Just add in > as an argument to sort-by:

  (->> (string/split s #"\s+")
       frequencies
       (sort-by val >)
       (take 10))
Just mentioning it here because I find it vastly more readable than (comp - val).

Re: LINQ Ruined My Favorite Interview Question

#95

Post by MichaelGG »

joshuaellinger wrote: post #2

I am a big fan of LINQ but it gives and takes away complexity at the same time. It makes a 'whole class of things that you would have to do with loops' go away. Once you are comfortable with the syntax, it makes code a lot more readable. But you lose track of when and where things are getting executed. For example, it is easy to make something that you intend to execute inside of SQL server run inside of C# code. And…

The "execute inside SQL but ends up in C#" is because of the terrible decision of the C# language designers to make reified code (expression trees) have the exact same syntax as lambda functions that are normal code.

If you had to tell the compile if you wanted code or a tree, that problem would be solved. It'd also be one step closer to allowing type inference for lambdas assigned to locals.

Re: LINQ Ruined My Favorite Interview Question

#96

Post by epistasis »

kephra wrote: post #7

/me wonders are candidates allowed to chose their favorite language? man bash | tr '[:upper:] ' '[:lower:]\n' | sed '/^$/d' | sort | uniq -c | sort -rn | head | awk '{ print $2 }' | fmt or do you only hire windows coders?

This is how I do this sort of thing all the time. But, the sort is O(n log n), so it's asymptotically less satisfying.

Re: LINQ Ruined My Favorite Interview Question

#97

Post by wiredfool »

shill wrote: post #31
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 ?!?

Without imports: d = {} for word in s1.split(' '): try: d[word] += 1 except KeyError: d[word] = 1 print [(x, d[x]) for x in sorted(d, key=d.get, reverse=True)][:10]

Or, use a defaultdict(int), or more in line with yours:

d[word] = d.get(word,0) + 1

dictionary.get is quite useful.

Also, I'd consider s.split(None), instead of s.split(' '). It will group whitespace, so that any double space or other whitespace is collapsed into one delimiter.

Re: LINQ Ruined My Favorite Interview Question

#98

Post by tolmasky »

My main problem with LINQ is that it seems to perform terribly on mobile. I was looking for map/reduce/etc type functions for C# in Unity, and thought I found it with LINQ. To my dismay, LINQ creates so many crazy intermediate objects to pull off its "laziness" that our GC high water mark was being crossed all the time. I went and just reimplemented everything from underscore.js in C# and got way better performance. I imagine this is probably not an issue on desktops/servers.

Re: LINQ Ruined My Favorite Interview Question

#99

Post by Locke1689 »

tolmasky wrote: post #98

My main problem with LINQ is that it seems to perform terribly on mobile. I was looking for map/reduce/etc type functions for C# in Unity, and thought I found it with LINQ. To my dismay, LINQ creates so many crazy intermediate objects to pull off its "laziness" that our GC high water mark was being crossed all the time. I went and just reimplemented everything from underscore.js in C# and got way better performance.…

If you'd like to share your code, I'm a functional programmer at heart and am always looking for optimization opportunities for functional-style programming in C#. If you send me some of the code you were having trouble with I can see if your use case maps well into some compiler optimization strategies.

Re: LINQ Ruined My Favorite Interview Question

#100

Post by spenuke »

shill wrote: post #93
spenuke wrote: post #68

Earlier quoted context omitted.

I'm a newbie, but the question seemed approachable so I went for it. This is what I came up with. (Python, btw.) def top_ten(s): words = s.split(' ') word_list = set(words) return sorted(word_list, key=lambda x: words.count(x))[:10] The question didn't ask for word counts, so I didn't see the need for a dictionary. I'd appreciate any advice on my solution. I'd be thrilled if I'm not too far off from being capable of…

> I'd appreciate any advice on my solution. You should always compare your results to what is expected. For a problem like this, use a small set of test data that can easily be counted and sorted in your head or on paper. You forgot reverse=True and your results show the 10 least common words. ;) This kind of error happens to all of us. That's why we have unit tests and QA teams. If you made this mistake during an in…

Ha, nice! Funny you should mention that. I did exactly that when tooling around in the repl and forgot the reverse kw, saw something fishy, and fixed it. Promptly forgot it again when I typed it in this comment. :)
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