Re: delete columns csv file

r wrote:
> On Apr 16, 4:16 pm, Janis <janis_papanag...@[EMAIL PROTECTED]
> wrote:
> 
>>>Returning to my example: sorry to re-start with this issue of reading
>>>the file twice, would you direct me towards the section of the gawk
>>>guide that explains what you call a "2-pass solution". I'd like to
>>>learn the gawk technical phrase for this task and read the background.
>>
>>That has nothing to do with gawk. Many tools operate on data streams
>>sequentially but have tasks to do that can only be completed if the
>>data is already fully known to them; so you read the same file twice.
>>In awk that can be done by providing the filename two times in the
>>argument list.
>>
>>  awk -f awkprog  datafile  datafile
> 
> 
> Thanks; the only analogy I can think of is when I create my dvi file
> from activating my latex command twice. Interesting to know of this
> requirement to read a file twice.

It's a natural requirement for any program that does no implicit
rewrites/resets or random access (seeks) on a file. Basically,
awk is a filter program that reads streams of data sequentially.

> 
> 
>>
>>>Similarly, I've understood the terms NR and FNR but could not find
>>>reference to the equation NR==FNR, which section of the gawk guide
>>
>>It's just the equality operator as known from mathematics.
>>
>>Since you know what each variable means you just have to think about
>>the values they will take while awk is processing the first file and
>>while processing the second file.
>>
>>
>>>should I read to learn that it is possible to conceive this equation?
>>>As a complete novice, where do I learn that after learning the
>>>definition of NR and FNR independently, it is possible to use these
>>>functions with ==?
>>
>>You can compare values of the same type most generally.
>>(Sometimes awk performs implicit conversions before comparison.)
>>
> 
> Is there a definitive list of types of values where awk makes implicit
> conversions, or is this of relative minor importance to me?

It is of minor importance to you at your current level of knowledge
about awk, I suppose. But it's basic knowledge, anyway. The list is:
numbers and text strings. (If you're interested have also a look at
explicit conversions from numbers to strings and vice versa; str+0,
num"".)

> 
> 
> 
>>>The gawk guide introduces the term 'i++' in section 1.3 but '++' is
>>>explained (correctly?) as increment operator in section 5.8? Why is
>>>increment necessary in this example?
>>
>>The ++ is the increment operator. You need a variable to increment.
>>Here i is the name of the variable to increment.
>>
>>(To explain the necessity in "the" example I'd need the context.)
>>
> 
> The example I cite is in my first message that created this topic of
> discussion.

It's good style (and a sign of respect for the people trying to help
you) to quote enough context to make any posting self-contained.

> 
>>>So far, apart from my failure to understand NR==FNR, I understand as
>>
>>NR==FNR is true while you're processing the first file of the
>>argument list. If the same filename is given twice then you can
>>call that condition "first pass" on the file.
>>
> 
> 
>>All that are really the basic basics of the awk language;
>>I'd suggest to read some more of the GNU awk guidebook.
> 
> 
> I'm on to it when time permits! :)

Good luck.

Janis