Yes - in R, negative indexes remove the item with that (positive) index, e.g. from this R session (where ">" is the input prompt):
> vv<-(1:5); > vv [1] 1 2 3 4 5 > vv[-3]; [1] 1 2 4 5 > vv[c(-2,-5)]; [1] 1 3 4 On Tue, Sep 2, 2014 at 3:23 PM, Vijay Lulla <[email protected]> wrote: > Yes, that's what I meant. Try selecting first and last n rows from data > frame. Actually R's indexing ([) is very lax and can trump people (at least > it has me) in strange ways. http://adv-r.had.co.nz/Subsetting.html How > about subsetting with floats? J raises 'domain error'...R > does...<quote>Numeric values are coerced to integer as by 'as.integer' (and > hence truncated towards zero).</quote> I know this because I've made this > mistake a couple of times! > > One of the things that I really like about J is how regular it is....at > least after you get *slightly more* comfortable with it. > > > On Tue, Sep 2, 2014 at 3:00 PM, Devon McCormick <[email protected]> > wrote: > > > I think he means this by "mixing +ve and -ve": > > 0 1 _2 _1 { i.10 > > 0 1 8 9 > > > > > > On Tue, Sep 2, 2014 at 2:50 PM, Joe Bogner <[email protected]> wrote: > > > > > I also use { extensively (dyadic). I appreciate the challenge of > > > coming up with a minimal list. One criteria may be: can it be done > > > relatively easily with one of the other operations? > > > > > > For {, it's fairly easy to use {. and }.... > > > > > > For example: {. 3 }. 0 1 2 3 4 5 > > > > > > With a trivial case, the performance is negligible, but perhaps not as > > > readable > > > > > > 100 timespacex '{. 9999999 }. i. 1e7' > > > 0.0248935 1.3422e8 > > > > > > 100 timespacex '9999999 { i. 1e7' > > > 0.0269468 1.3422e8 > > > > > > I mostly use it for simple indexing. I didn't understand your comment > > > about mixing +ve and -ve. Can you elaborate? > > > > > > [by the way, excellent list Devon. I may use it to extend my > > > coffeescript implementation of APL to have functioning examples for > > > each of those operations] > > > > > > > > > > > > On Tue, Sep 2, 2014 at 2:39 PM, Vijay Lulla <[email protected]> > > wrote: > > > > Just out of curiosity, why is { not included? I use it extensively > for > > > my J > > > > explorations. Also, it is much more regular and useful(flexible?) > than > > > > indexing in other languages. For e.g., You cannot mix +ve and -ve > > indexes > > > > in R but it works as expected (at least for me) in J. Regardless, > nice > > > work. > > > > > > > > Thanks, > > > > Vijay. > > > > > > > > > > > > On Tue, Sep 2, 2014 at 1:16 PM, Devon McCormick <[email protected]> > > > wrote: > > > > > > > >> Based on Skip's suggestion, this page is now here - > > > >> http://www.jsoftware.com/jwiki/DevonMcCormick/MinimalBeginningJ - > and > > > is > > > >> titled "Minimal J for Beginners". > > > >> > > > >> > > > >> On Tue, Sep 2, 2014 at 1:10 PM, Devon McCormick <[email protected] > > > > > >> wrote: > > > >> > > > >> > Good point - I picked up the "J Kernel" label from the discussion. > > > >> > > > > >> > > > > >> > On Tue, Sep 2, 2014 at 12:36 PM, Skip Cave < > [email protected] > > > > > > >> > wrote: > > > >> > > > > >> >> Devon, nice job of putting together a reduced set of primitives > for > > > rhe > > > >> >> beginner. The only issue I see is the name. As a beginner, I > would > > > never > > > >> >> think to find a set of most-commonly-used primitives under the > name > > > "J > > > >> >> Kernel" That actually sounds like a discussion of the internals > of > > J, > > > >> >> which > > > >> >> is what I thought when I read the subject of your email. I doubt > > > that a > > > >> >> beginner would check out a page with that label. A title like > "J's > > > Basic > > > >> >> Commands for Beginners" or equivalent, would be more likely to > > > attract > > > >> the > > > >> >> intended audience. > > > >> >> > > > >> >> Skp > > > >> >> > > > >> >> Skip Cave > > > >> >> Cave Consulting LLC > > > >> >> > > > >> >> > > > >> >> On Tue, Sep 2, 2014 at 9:54 AM, Devon McCormick < > > [email protected]> > > > >> >> wrote: > > > >> >> > > > >> >> > Based on some feedback from Greg Borota last year on his > > > experiences > > > >> >> > learning J, I've put together a page on the J Wiki - > > > >> >> > http://www.jsoftware.com/jwiki/DevonMcCormick/JKernel - that > > has a > > > >> few > > > >> >> > selected things from J on which a beginner can concentrate to > > avoid > > > >> >> being > > > >> >> > overwhelmed by the language in full. > > > >> >> > > > > >> >> > It's a pretty bare minimum and I couldn't find a good link that > > > >> explains > > > >> >> > J's use of single quote for quoted strings but everyone should > > feel > > > >> >> free to > > > >> >> > add to it - sparingly, as it's supposed to be a reduced set of > > the > > > >> >> > language. > > > >> >> > > > > >> >> > It might make sense to leave the existing page much as it is > and > > to > > > >> >> think > > > >> >> > about a 2nd tier of slightly more advanced verbs and such. > There > > > were > > > >> >> good > > > >> >> > suggestions in the original discussion - > > > >> >> > > > > >> >> > > > > >> >> > > > >> > > > > > > http://jsoftware.2058.n7.nabble.com/Learning-J-language-initial-thoughts-td52786.html#a52793 > > > >> >> > - that I elided as I consider them more than the bare minimum > > > (things > > > >> >> like > > > >> >> > rank modifiers and logic verbs). > > > >> >> > > > > >> >> > -- > > > >> >> > Devon McCormick, CFA > > > >> >> > > > > ---------------------------------------------------------------------- > > > >> >> > For information about J forums see > > > >> http://www.jsoftware.com/forums.htm > > > >> >> > > > > >> >> > > > ---------------------------------------------------------------------- > > > >> >> For information about J forums see > > > http://www.jsoftware.com/forums.htm > > > >> >> > > > >> > > > > >> > > > > >> > > > > >> > -- > > > >> > Devon McCormick, CFA > > > >> > > > > >> > > > > >> > > > >> > > > >> -- > > > >> Devon McCormick, CFA > > > >> > ---------------------------------------------------------------------- > > > >> For information about J forums see > > http://www.jsoftware.com/forums.htm > > > >> > > > > > ---------------------------------------------------------------------- > > > > For information about J forums see > http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > > > > > > > -- > > Devon McCormick, CFA > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > -- Devon McCormick, CFA ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
