[erlang-questions] increment in map

Wes James <>
Mon Jul 26 22:36:11 CEST 2010


Thanks.  That worked.  Didn't someone mention the other day on the
list that if we could remember the available BIFS and what they do,
we'd be set??

-wes

On Mon, Jul 26, 2010 at 1:51 PM, Gleb Peregud <> wrote:
> [{td, [],[W,X]} || {W, X} <- lists:zip([1,2,3], [1,2,3])]
>
> On Mon, Jul 26, 2010 at 21:43, Wes James <> wrote:
>> Nicholas,
>>
>> Thx - I realize I asked the question wrong.  The list comprehension
>>
>>  [{td, [], massage(W,Ls)} || W <- vp(Vp,Row)]
>>
>> will create a list in place, is there a way to create an increment
>> value within this structure?
>>
>> I looked at a quick test with:
>>
>> [{td, [],[W,X]} || W <- [1,2,3], X <- [1,2,3]]
>>
>> but it creates:
>>
>> [{td,[],[1,1]},
>>  {td,[],[1,2]},
>>  {td,[],[1,3]},
>>  {td,[],[2,1]},
>>  {td,[],[2,2]},
>>  {td,[],[2,3]},
>>  {td,[],[3,1]},
>>  {td,[],[3,2]},
>>  {td,[],[3,3]}]
>>
>> whereas, I would like a one to one paring:
>>
>> [{td,[],[1,1]},
>>  {td,[],[2,2]},
>>  {td,[],[3,3]}]
>>
>>
>> -wes
>>
>> On Mon, Jul 26, 2010 at 1:25 PM, Nicholas Frechette <> wrote:
>>> You could use 'foldl' instead of map:
>>> foldl(fun(Row, Inc) ->
>>>     ...
>>>     Inc + 1 %% Return value is the new value of Inc for the next call
>>>     end, Rows, 0).
>>>
>>> You could also zip seq(0, numrows) with your rows and unzip them inside the
>>> map (though if you have a lot of rows, the above will be faster and leaner).
>>>
>>> Nicholas
>>>
>>> On Mon, Jul 26, 2010 at 2:38 PM, Wes James <> wrote:
>>>>
>>>> I have this code:
>>>>
>>>>  map(fun(Row) ->
>>>>                {table, [{style, "width:700px; margin:5px;
>>>> background-color:dddddd;"}],
>>>>                        [
>>>>                        thtd(Hdrs, [{td, [], massage(W,Ls)} || W <-
>>>> vp(Vp,Row)])
>>>>                ]}
>>>>                        end, Rows)
>>>>
>>>> and as I loop through the Row I would also like to send an increment
>>>> in the massage(W,LS,Inc) call, but I don't see how I can do that
>>>> within a list comprehension.  Any ideas on how I would do this?
>>>>
>>>> thx,
>>>>
>>>> -wes
>>>>
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>>>
>>>
>>
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