On Mon, Jun 18, 2012 at 5:15 AM, Gian Medri <gianme...@gmail.com> wrote:
> I shall replace some text in a vector. My function is
> Replace=:13 :'(p{.y),(>1{x),(($>0{x)+p=.I. (>0{x) E. y)}.y'
> Example : ('can be';'is') Replace 'Life can be good'
> Life is good
> I would like to see if there is a better solution, more J-like.
"Better" needs to be defined before it can be achieved. There are all
sorts of "better". Perhaps of interest, however, are the functions
made available using
require 'regex'
(also:
open 'regex'
lets you view the file from J6, it does not work in some versions of
J7 but may work in some versions?).
> I have also 2 functions for interval:
> 1) int1=:({.@] < [)*.([ < {:@])
> 6 int1 4 9
> 1
> This is very clear how it works.
>
> 2) int2=:[: ~:/ >:/~
> This is more concise and elegant, but I don't understand how it works.
> Can somebody give me an explanation?
I did not see anyone give the sort of explanation which I prefer,
which is to break the execution down into steps.
6 ([: ~:/ >:/~) 4 9
1
first computes the value prescribed by the right tine of the fork:
6 (>:/~) 4 9
0 1
and the ~ swaps arguments of its verb, so this is equivalent to
4 9 (>:/) 6
0 1
also the / is irrelevant here (we are using a verb it derived in a
dyadic context and one of the dyadic arguments is rank 0). So:
4 9 (>:) 6
0 1
in other words the first thing we find is that 4 is not greater than
or equal to 6 but 9 is.
And then we process this intermediate result
~:/ 0 1
1
The / adverb inserts its verb between each item of its argument, so
this is equivalent to
0 ~: 1
1
In other words, the statement is true when the right argument is
greater than one of the left argument values but not the other.
Stepping back, the / in the right tine would be useful when we have
multiple values in the right argument:
2 3 5 7 11 ([: ~:/ >:/~) 4 9
0 0 1 1 0
Here, instead of eliminating the rightmost /, I would note that we are
finding the result of >: for all paired elements from the left and
right arguments of the verb derived by / when its dyadic definition is
used.
Finally, note that we can test against multiple intervals if we
arrange them properly:
2 3 5 7 11 ([: ~:/ >:/~) 1 5,.4 9,.6 10
1 1 1 0 0
0 0 1 1 0
0 0 0 1 0
I hope this helps,
--
Raul
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