[Jprogramming] Need better understanding of "from"

['robert therriault' via Programming]

Hi Harvey,

>> What I'm trying to do is to grab 2 letters at a time in sequence
>> through the 6-character combined planetary abbreviations for 3
>> planets.  Is there another way?

I think what you want is dyadic \ (Infix https://code.jsoftware.com/wiki/Vocabulary/bslash#dyadic)

    planets=. 'mevema'
   _2 [\ planets  NB. negative left operand means take n at a time without overlapping
me
ve
ma
   2 [\ planets  NB. positive left operand means take n at a time with overlapping and potential shards at the end
me
ev
ve
em
ma

you could put any monadic verb that you want in place of the [ (Same), often used with < (Box)

   _2 <\ planets  NB. boxes two at a time without overlapping
┌──┬──┬──┐
│me│ve│ma│
└──┴──┴──┘

Cheers, bob

> On Apr 13, 2021, at 03:16, 'Mike Day' via Programming <programming at jsoftware.com> wrote:
> 
> My variant:
> 
>   j =. 1
>   'mevema' {~ 0 1 + +: j
> ve
> 
> I use {~ quite often,  possibly thanks to nostalgia for [i]  !
> 
> Mike
> 
> Sent from my iPad
> 
>> On 13 Apr 2021, at 09:14, HH PackRat <hhpackrat at gmail.com> wrote:
>> 
>> Hello, all!
>> 
>> I'm stumped and need to know why the following "from" problem occurs
>> and how to do what I'd like to do:
>> 
>> No problem when numeric values are used:
>>  val=. 0 1 { 'mevema'
>> me
>>  val=. 2 3 { 'mevema'
>> ve
>> 
>> Problem when formulas are used instead of numeric values:
>>  j=. 0   [or 1 or 2]
>>  val=. (2*j) (1+2*j) { 'mevema'
>> |syntax error
>> |   val=.    (2*j)(1+(2*j)){'mevema'
>> 
>> Why does "from" work with numeric values but not with formulaic
>> versions of those same values for use inside a "for_j" loop to handle
>> multiple cases?
>> 
>> What I'm trying to do is to grab 2 letters at a time in sequence
>> through the 6-character combined planetary abbreviations for 3
>> planets.  Is there another way?  (Explicit code only, please, if you
>> give any examples.)
>> 
>> I just don't understand why one version works and the other doesn't.
>> Any help appreciated!
>> 
>> Harvey
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