Feel free to ask follow-up questions on the basics privately, since many Clojure programmers are probably already familiar with them, whereas follow-up questions on persistent data structures are very on-topic, since I would guess many people who have studied computer science and/or programming for a while may not be familiar with them.
The classic model of an array is based upon the implementation of physical RAM in a computer: a physical RAM, at a high level and leaving out details of variations, is a device where you either give it a command READ and an address, and it returns an 8-bit byte stored at that location, or you give it a WRITE command, an address, and an 8-bit value, and it stores the 8-bit value at the location given by the address. A classic array is a one-dimensional structure indexed by an integer i, usually from 0 up to some maximum value N, and every item in the array stores an item of the same size and type, e.g. all 32-bit integers, or all pointers to some object elsewhere in the memory. If every item fits in exactly B bytes, and the first item of the array begins at address A in the memory, then item i will be at address A+B*i in the memory. In terms of performance, computers are designed to be able to access any address in their memory in the same amount of time, no matter what address it is stored at, so with a couple of instructions to calculate A+B*i, the computer can read or write any element of an array within a constant amount of time (constant meaning it doesn't get larger or smaller depending upon the size of the array -- it is always the same no matter the array's size). With other non-array data structures like trees, accessing an element takes longer as the data structure grows to contain more items. I don't recall if it covers persistent data structures like the ones most commonly used in Clojure, but Cormen, Leiserson, and Rivest's "Introduction to Algorithms" is used in many colleges as a text in courses on algorithms and data structures. There are probably other books that would be better as a "primer", and it does assume you are comfortable with at least algebra and a bit more math, but if you got through a chapter of it and understood even half of it, you'd have learned something worth knowing about the subject. http://www.amazon.com/Introduction-Algorithms-Includes-CD-Rom-Thomas/dp/0072970545/ref=sr_1_2?ie=UTF8&qid=1332128117&sr=8-2 There is a newer edition than the one I linked to, but an older used copy for $25.00 might be closer to what you want if you aren't sure yet. Andy On Mar 15, 2012, at 12:15 PM, Nic Long wrote: > Hi all, > > I am starting to learn Clojure after buying the book 7 Languages in 7 > Weeks (really interesting read) and working through the examples > there. But my background is PHP (and no Computer Science degree) so my > understanding of data structures and in general, my understanding of > low-level CS ideas, is pretty limited to say the least - PHP only has > arrays (which I read are only 'ordered hash tables' in fact) and > objects so I've never had to think hard about which data structures to > use, nor how they actually work. > > So I guess I'm asking whether anyone can recommend some good primers > on data structures, both as they relate to Clojure, but also how they > work in the fundamentals - e.g. what exactly is the classic model of > an 'array' and how does it work, etc. I have read the various > performance commitments for the data-types in Clojure on the .org site > but even things like Big O notation are still pretty new to me. > > I'm sure this stuff is pretty basic for many, but I don't know it and > would like to! > > I'm not afraid of some heavy reading; I'd rather get a really deep and > solid grasp of the fundamentals, then a quick surface-level solution. > If I'm to develop as a programmer I feel like I need to get looking > under the hood as it were, even though I can get by in PHP (for the > most part anyway) without this kind of understanding. > > Thanks in advance, > > Nic > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with your > first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
