hi,

"lmap" is a new command to tcl able to filter lists BUT missing the
feature to work an "stride" lists.

a stride list is a list with a pattern of multiple items.
example: The "array get…" produce a flat list of stride of "2"

code: lmap {k v} $packageDEF {list $k [lindex $v 1]}

packageDEF is a stride-2 list (k v) with "v" is a list
and I want to filter from "v" the index=1 argument

the code above create a list of lists:

> {k1 v11} {k2 v21} …

but I want to have

> k1 v11 k2 v22 …

The problem is the "list" command used to return TWO values from
filer-code. The NEW syntax would be:

code: lmap -stride 2 {k v} $packageDEF {list $k [lindex $v 1]}

> k1 v11 k2 v22 …

mfg AO

On 20.05.22 12:13, aotto1968 wrote:
> > k1 v11 k2 v22 …

correct: I want to have: > k1 v11 k2 v21!! …

Am 20.05.22 um 12:13 schrieb aotto1968:
> hi,
>
> "lmap" is a new command to tcl able to filter lists BUT missing the
> feature to work an "stride" lists.
>
> a stride list is a list with a pattern of multiple items.
> example: The "array get…" produce a flat list of stride of "2"
>
> code: lmap {k v} $packageDEF {list $k [lindex $v 1]}
>
> packageDEF is a stride-2 list (k v) with "v" is a list
> and I want to filter from "v" the index=1 argument
>
> the code above create a list of lists:
>
> > {k1 v11} {k2 v21} …
>
> but I want to have
>
> > k1 v11 k2 v22 …
>
> The problem is the "list" command used to return TWO values from
> filer-code. The NEW syntax would be:
>
> code: lmap -stride 2 {k v} $packageDEF {list $k [lindex $v 1]}
>
> > k1 v11 k2 v22 …

And what would be returned if someone does:

lmap -stride 3 {k v} $packageDEF {list $k [lindex $v 1]}

?

Or even with vayrying list lengths in the "lmap kernel"?
What you're after can be achieved at the moment using:

concat {*}[lmap .... ]

Instead of "-stride" which would be hard to interpret for the case of
building a list (as opposed to reading/traversing), I'd much rather see
a "-flatten" switch which does concat the lists instead of appending
into a new list.

Christian

Am 20.05.22 um 18:44 schrieb Christian Gollwitzer:
>> The problem is the "list" command used to return TWO values from
>> filer-code. The NEW syntax would be:
>>
>> code: lmap -stride 2 {k v} $packageDEF {list $k [lindex $v 1]}
>>
>>  > k1 v11 k2 v22an…
>

ah, and for the special case of transforming a key-value list where only
the value is changed, there is "dict map" which does that. Your example
would be:

dict map {k v} $packageDEF {lindex $v 1}

Christian

On 20.05.22 18:44, Christian Gollwitzer wrote:
~~
>
> And what would be returned if someone does:
>
>
> lmap -stride 3 {k v} $packageDEF {list $k [lindex $v 1]}
>
> ?
>
> Or even with vayrying list lengths in the "lmap kernel"?
> What you're after can be achieved at the moment using:
>
>     concat {*}[lmap .... ]
>
> Instead of "-stride" which would be hard to interpret for the case of
> building a list (as opposed to reading/traversing), I'd much rather see
> a "-flatten" switch which does concat the lists instead of appending
> into a new list.
>
>     Christian

I thing the -stride 3 is not a problem because returning a
list-of-length-3 from the filter is an easy condition to test. If this
condition is NOT ok than raise an error.

mfg.

On 20.05.22 18:47, Christian Gollwitzer wrote:
> Am 20.05.22 um 18:44 schrieb Christian Gollwitzer:
>>> The problem is the "list" command used to return TWO values from
>>> filer-code. The NEW syntax would be:
>>>
>>> code: lmap -stride 2 {k v} $packageDEF {list $k [lindex $v 1]}
>>>
>>>  > k1 v11 k2 v22an…
>>
>
> ah, and for the special case of transforming a key-value list where only
> the value is changed, there is "dict map" which does that. Your example
> would be:
>
>     dict map {k v} $packageDEF {lindex $v 1}
>
> Christian

ok, for stride-2 this is a possible solution but how expensive it is to
build a dict?

performance | dict : list → dict → filter → dict → list
performance | -stride 2 : list → filter → list

mfg AO