[R] What to use for assignment, = or - ?
I've noticed an increasing tendency for people to use '=' rather than the older '-' symbol. When '=' became available as an assignment operator in S-PLUS in the late '90s my first reaction was to switch to it as well. Brian Ripley warned me that it was not a good idea. As usual he was right, but it took a couple of pretty serious finger-burning episodes before I came fully around to his view. There are three left assignment operators in S, and it's a good idea to distinguish what they do. a - b assigns a value 'b' to an object 'a' in some parent environment a - b assigns a value 'b' to an object 'a' in the current environment a = b (inside the argument list of a function call) potentially assigns a value 'b' to an object 'a' in the child environment of the function. Lazy evaluation determines if it actually happens or not. You must use '=' for the third of these. If you choose to use it for the second as well, as is allowed, there is a danger that you will confuse the environment in which the assignment is actually made. It's not a great danger, of course, but it can happen. In any case, it is a good idea to use three separate operators for these three distinct purposes, if nothing else as a clear visual reminder of what kind of assignment is intended to take place. I suspect the push towards using '=' instead of '-' has two main drivers: 1. the world is full of lazy typists 2. right now there seems to be a big influx of Matlab people into R, and it makes them feel more at home. Neither of these is much of a reason, I reckon. Bill Venables CSIRO Laboratories PO Box 120, Cleveland, 4163 AUSTRALIA Office Phone (email preferred): +61 7 3826 7251 Fax (if absolutely necessary): +61 7 3826 7304 Mobile: +61 4 8819 4402 Home Phone: +61 7 3286 7700 mailto:[EMAIL PROTECTED] http://www.cmis.csiro.au/bill.venables/ __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] What to use for assignment, = or - ?
Bill.Venables at csiro.au writes: I've noticed an increasing tendency for people to use '=' rather than the older '-' symbol. When '=' became available as an assignment operator in S-PLUS in the late '90s my first reaction was to switch to it as well. Brian Ripley warned me that it was not a good idea. As usual he was right, but it took a couple of pretty serious finger-burning episodes before I came fully around to his view. [snip] I suspect the push towards using '=' instead of '-' has two main drivers: 1. the world is full of lazy typists 2. right now there seems to be a big influx of Matlab people into R, and it makes them feel more at home. Neither of these is much of a reason, I reckon. It may not be a good reason, but the reason I usually teach = rather than - to my students is that they are usually learning scripting/programming for the very first time, and the = syntax for assignment (which as I recall was called gozzinta, for goes into, in the FORTRAN coloring book) seems natural to most people (even though it's logically quite different). They are so overwhelmed by learning new things that I don't want to add one more. (This is admittedly a judgment call.) Ben Bolker __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] What to use for assignment, = or - ?
On Apr 6, 2008, at 10:35 AM, Ben Bolker wrote: Bill.Venables at csiro.au writes: I've noticed an increasing tendency for people to use '=' rather than the older '-' symbol. When '=' became available as an assignment operator in S-PLUS in the late '90s my first reaction was to switch to it as well. Brian Ripley warned me that it was not a good idea. As usual he was right, but it took a couple of pretty serious finger-burning episodes before I came fully around to his view. [snip] I suspect the push towards using '=' instead of '-' has two main drivers: 1. the world is full of lazy typists 2. right now there seems to be a big influx of Matlab people into R, and it makes them feel more at home. Neither of these is much of a reason, I reckon. It may not be a good reason, but the reason I usually teach = rather than - to my students is that they are usually learning scripting/programming for the very first time, and the = syntax for assignment (which as I recall was called gozzinta, for goes into, in the FORTRAN coloring book) seems natural to most people (even though it's logically quite different). They are so overwhelmed by learning new things that I don't want to add one more. (This is admittedly a judgment call.) I actually teach my students to use -, for a number of reasons, but in some sense for the same reason you choose to teach = instead: I feel that - expresses better the act of assigning. The problem really is that in mathematics we use = to denote both assignment and equality, and are forced to use words like let and define to indicate when an assignment is meant, which I suppose is not the norm. In other words, which one is meant is based on context. Context is perhaps a reasonable way to define things in mathematics, or most other non-programming settings really, but it is definitely not a very good way in programming settings, in my opinion. This is the problem with = in this case: It has different meanings depending on its context. This can lead to subtle errors, not easy to track down. On another level, - brings up the severity of the act of assignment more clearly. You are about to overwrite whatever meaning that symbol had in the past, and replace it with a brand new meaning, and this can have a number of quite unpredictable side-effects. So it is not something that should be done lightly. In my opinion assignments should be used sparingly. Now, you might argue that when students are first learning programming, we should make it as simple as possible for them. Though I do respect that view, I think it is also important to not teach them bad practices, and overdoing it on the assignments is such a bad practice, IMO. It's hard to change what one has learned early on and gotten used to. I've spent a lot of my teaching time trying to correct such bad habits on the part of my students, especially on the importance of making it clear, when writing down an equation, whether that equation is something we know, something we are trying to prove, or used as a definition for the LHS of it. That's my story anyway, and I'm sticking to it. Sorry if I strayed a bit off topic there Ben Bolker Haris Skiadas Department of Mathematics and Computer Science Hanover College __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
