Having too many many "For" loop in my code increase complexity to my development, is there a better solution to For loop alternative?
In my code. I have used 50% of the time to loop array.
Well if you have to work on Arrays alot check the reference under Array. They have very usefull functions like Array.every() or Array.forEach() or Array.map().
Maybe one of those is helpful to your concern.
Well, there's for each and while, but they're still loops!
Sometimes, looping is just necessary, and there's no way around it. Can you explain more about what you think is wrong with your current code, or perhaps post a code sample?
On the contrary, if you use the same loop style throughout the application, it may make it easier to read for third parties.
Related
I'm wondering if anyone has figured out how to make the WKInterfacePicker repeat after the last item, so that it forms a continuous loop? I know this is possible with UIPickerView in UIKit, but like most WatchKit objects WKInterfacePicker has very limited accessibility.
One work-around I figured is to have a long list of WKPickerItem of repeating items. You want it REALLY LONG, so that it wears the patience of even the naughtiest users who try to catch you cheating.
You can always determine the desired index by simple modulo operation.
Well, I'm also looking for a better answer to reveal the official way of doing this...
I'm looking for something like this:
virtualArray = VirtualArray((parent1,2:5,1:3), (parent2,1:15,5:7))
which would construct something like the SubArray, except with contributions from two or more parent arrays.
The point is to combine two or more array-like data sources without allocating additional memory.
I'm aware of both the SubArray and View types, which provide access to a slice of a parent array. I've also come across the DistributedArray and SharedArray, which looks like I could hack to make do what I want, but that doesn't seem to be the intended purpose of these types.
I could try to implement myself, but I don't want to reinvent the wheel if someone else has already done it, probably much better than I could at this point.
The short answer: there's no complete solution for this at the moment. It's a tricky problem to make both fast and generalized. I asked this question recently on julia-users... you might find some ideas there.
I've been looking for a proper implementation of hash map in R, with functionalities similar to the map type in Python.
After some googling and searching the R documentations, I found that environment and named list are the ONLY options I can use (is that really so?).
But the problem with the two is that they can only take charaters as key for the hashing, not even a number, let alone other type of things.
So is there a way to use arbitrary things as key? or at least more than just characters.
Or is there a better implemtation of hash map that I didn't find with better functionalities ?
Thanks in advance.
Edit:
My current problem: I need a map to store the distance relationship between data points. That is, the key of the map is a tuple (p1, p2) and the value is a number.
The reason I asked a generic question instead of a concrete one is that I'm learning R recently and I want to know how to manipulate some of the most fundamental data structures, not only what my problem refers to. So I may need to use other things as key in the future, and I want to avoid asking similar questions with only minor difference every time I run into them.
Edit 2:
I got a lot of very good advices on this topic. It seems I'm still thinking quite in the Pythonic way, rather than the should-be R way. I should really get more R-ly ! I think my purpose can easily be satisfied by a matrix in R. Thanks All !
The reason people keep asking you for a specific example is that most problems for which hash tables are the appropriate technique in Python have a good solution in R that does not involve hash tables.
That said, there are certainly times when a real hash table is useful in R, and I recommend you check out the hash package for R. It uses environments as its base but lets you do a lot of R-like vector work with them. It's efficient and I've never run into a problem with it.
Just keep in mind that if you're using hash tables a lot while working with R and your code is running slowly or is buggy, you may be able to get some mileage from figuring out a more R-like way of doing it :)
My questions is basically all in the title. I have no real application in mind, I'm just trying to make sure I use generally accepted good coding practices, and I remember my CS professor saying that breaks are generally avoided when possible, but he never told us why.
I would ask him myself, but he's out of his office this summer.
This is a theological issue. People who are opposed to the use of break (or continue for that matter) say that it makes the control flow of the program harder to follow and thus makes the program less readable. But an easier way to make readable code is simply to make shorter functions, use meaningful variable names, comment appropriately, etc.
Sometimes professors are wrong.
He may object to skipping out of a loop right in the middle of it. This is akin to using a return statement in the middle of a function...some consider that blasphemy.
What ever is the simplest, and produces the most easily maintainable code, is what should be used.
Generally speaking, you will use 'break' to get out of cycles when a certain condition is met (for instance, when you've found what you're looking for, etc.); I don't consider it 'evil' such as the infamous GOTO statement, but reasonable people will differ.
What Dijkstra said was harmful about goto statements - http://drdobbs.com/blogs/cpp/228700940
and https://softwareengineering.stackexchange.com/questions/58237/are-break-and-continue-bad-programming-practices
Your professor was saying "breaks should be avoided" because they are similar to the now-taboo goto statement. However to say "breaks should be avoided whenever possible" is just wrong.
Break exists for readability. You can do anything without break that you can with it, but that doesn't mean you should. Sometimes it just makes sense to make a statement like "In this condition, break out of this loop." or "In this condition, return from this function."
It's a bad idea to use break for program flow in a nested for loops in a way that might give a casual reader some confusion.
Simple rule of thumb: Does using break here (instead of additional if/thens, another boolean, etc.) make this easier to understand or harder to understand? It's that simple.
Ask your professor to try writing a switch statement in any C-style language without break. It can be done I'm sure, but the resulting code is not going to be any more readable.
switch (someExpression) {
case enumVar.CaseA:
// do things here, but don't you dare break!
case enumVar.CaseB:
// do other things - possibly unrelated or contradictory to CaseA
// ... and so on
}
Excuse my ignorance, as I'm not a computer engineer but with roots in biology. I have become a great fan of pre-allocating objects (kudos to SO and R inferno by Patrick Burns) and would like to improve my coding habits. In lieu of this fact, I've been thinking about writing more efficient functions and have the following question.
Is there any benefits in removing variables that will be overwritten at the start of the next loop, or is this just a waste of time? For the sake of argument, let's assume that the size of old and new variables is very similar or identical.
I think it will really depend on the specifics of the case. In some circumstances, when the object is large it might be a good idea to rm() it, especially if it is not needed and there are lots of other things to do before it gets overwritten. But then again, it's not impossible to conceive of circumstance were that strategy might be costly in terms of computation time.
The only way to know whether it would really be worthwhile is to try both ways and check with system.time().
No. Automatic garbage collection will take care of this just fine.