one problem it solves is simply not overtaking (on positive indexes). Sometimes what you can want.
the other problem it solves is returning i.0 if there are no items, and then leveraging other J functions interaction with i.0 as a parameter. one such interaction is in the last few examples I showed which is basically update_firstfewindexes_where function, but do nothing if the where clause returns no indexes. ----- Original Message ----- From: Raul Miller <[email protected]> To: Programming forum <[email protected]> Cc: Sent: Thursday, June 18, 2015 10:11 PM Subject: Re: [Jprogramming] recomendation for take I think you are trying to eliminate overtake - where the result is longer than the right argument. If that is the case, I do not think this definition achieves that: take =: (([ <. #@:]) {. ]) _6 take i.4 0 0 0 1 2 3 But here's a deeper question: what problem does this solve? Is this suggestion purely a matter of taste, or are there practical problems which are better solved this way? (If there are such problems, I'd be interested in hearing about them...) Thanks, -- Raul On Thu, Jun 18, 2015 at 10:00 PM, 'Pascal Jasmin' via Programming <[email protected]> wrote: > The verb take is defined in later versions of J as {. > > I recommend instead (this definition will not overwrite the one in z) > > take =: (([ <. #@:]) {. ]) > > 1 take i.2 NB. same as head > 0 > > 3 take i.2 > 0 1 > > > (i.0) -: 1 take i.0 > 1 > > > the reason this definition is better, is if you want the following, you can > still just use {. > > 3 {. i.2 > 0 1 0 > 1 {. i.0 > 0 > {. i.0 > 0 > > > my question is does anyone use the word take in code, such that it would > break under this redefinition? Even if you do, would you prefer having the > word take behave as above, and any code that depends on pure {. can just be > replaced with {. ? > > one of the reasons the code is useful (regardless of name) > > amdt =:2 : '(u (v{ ]))`(v"_)`]} ]' > > 2 + amdt (I.@:(2 < ])) i.5 NB. add 2 to items over 2 > 0 1 2 5 6 > > > 2 + amdt (I.@:(6 < ])) i.5 NB. no items pass filter, but no error, bc I. > returns i.0 > 0 1 2 3 4 > > > 2 + amdt (1 take I.@:(2 < ])) i.5 NB. just to first item over 2 > 0 1 2 5 4 > > 2 + amdt (2 take I.@:(1 < ])) i.5 NB. just to first 2 items over 1 > 0 1 4 5 4 > > > 2 + amdt (1 take I.@:(8 < ])) i.5 NB. no error. no unwanted updates > 0 1 2 3 4 > > > 2 + amdt (1 {. I.@:(8 < ])) i.5 NB. buggy - not intended > 2 1 2 3 4 > > 2 + amdt (2 {. I.@:(3 < ])) i.5 NB. buggy - not intended > 2 1 2 3 6 > ---------------------------------------------------------------------- > 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
