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Vim: how to delete every second row?

Answer 1

+3 A:

You should be able to use a macro:

http://www.oreillynet.com/mac/blog/2006/07/more%5Fvim%5Fsave%5Ftime%5Fwith%5Fmacros%5F1.html

Mark Wilkins 2009-12-22 14:40:04

Answer 2

+18 A:

You can use a macro for this. Do the following.

Start in command mode.
Go to the beginning of the file by pressing gg.
Press qq.
Click arrow down and press dd after.
Press q.
Press 10000@q

PS: To go to command mode just press Escape a couple of times.

ruibm 2009-12-22 14:40:42

Assuming your file is less than 20,000 line long of course :-)

paxdiablo 2009-12-22 14:55:26

+! to diablo, That's important otherwise you will go on deleting lines.

Michael Krelin - hacker 2009-12-22 14:58:13

Actually you are wrong Michael. This works flawlessly as VI will stop running the macro as soon as it hits end of file. You can very easily try it out with the sample above.

ruibm 2009-12-22 15:20:15

rui, my bad. twice as bad, actually - I also misread paxdiablo's comment. But, honestly, I still strongly dislike your answer for being unnecarily "complex" wrt keystrokes and non-universal.

Michael Krelin - hacker 2009-12-22 15:27:18

Well, like any macro you need to get it right the first time but after that you can apply to any file by just typing 10000@q. Either way I believe it's just a matter of tastes so I'm definitively not going to start a philosophical debate. :)

ruibm 2009-12-22 15:35:21

I prefer to use 'macro'. Using macro, you 'describe' how you would solve one particular task and let VIM repeat it for you. RUI, I would prefer to use 'j' instead of arrow key.

SolutionYogi 2009-12-22 17:29:40

Lol a valid point SolutionYogi I did think about that (cursors might not work if VI isn't configured properly), it's just that I never really got used to using h,j,k,l (this might sound like heresy). :)

ruibm 2009-12-22 18:12:25

rui, definitely. I actually revoked my downvote which was based on my mistake, not taste diffrences. I couldn't revoke it before because you had to edit your answer to allow it ;-) And yes, if I were to do it your way I'd also use 'j'. After all arrow escape sequence is so huge :) (I wonder is there a difference while *executing* recorded macro, not recording it?)

Michael Krelin - hacker 2009-12-22 19:55:19

Solution Yogi, actually, you can describe it in different ways. Like OP did - "delete every second row" (and this answer matches it perfectly) or "delete all even/odd rows". And it matters how you put it. That's why I think eloquence is one of the most important things for programmers. (and yes, I know I'm in danger now as I'm not writing my native language).

Michael Krelin - hacker 2009-12-22 20:25:02

To run a macro reliably across all lines of a file regardless of length you can use the :norm command:- 1,$norm! @q The norm runs normal mode commands from the command line and allows you to specify a line range which in this case is the entire file.

Andrew O'Reilly 2009-12-27 20:17:28

Answer 3

+6 A:

from vim mail archive:

:let i=1 | while i <= line('$') | if (i % 2) | exe i . "delete" | endif | let i += 1 | endwhile

(To be typed on one line on the vim command line, will delete row 1,3,5,7,...)

Fortega 2009-12-22 14:40:54

Then I'd prefer `!perl -ne 'print unless $. % 2'` :-)

Alex Brasetvik 2009-12-22 14:47:32

Alex, we think the same.

slim 2009-12-22 14:52:08

slim you think exactly the opposite!! (if vs. unless)

Michael Krelin - hacker 2009-12-22 15:01:08

And, Alex, I'd definitely prefer my solution to yours, but this one worth considering since this is the only sensible solution using only vim itself here.

Michael Krelin - hacker 2009-12-22 15:05:15

Answer 4

+5 A:

You can always pipe though a shell command, which means you can use any scripting language you like:

:%!perl -nle 'print if $. % 2'

(or use "unless" instead of "if", depending on which lines you want)

slim 2009-12-22 14:50:17

You don't need the `-l` switch to Perl... also, I'd say that `awk` is a little more widespread than Perl, though it's not really that much more these days, and can do this shorter: `:%!awk NR\%2`, or `:%!awk 1-NR\%2` for the other lines.

ephemient 2009-12-22 17:35:41

Answer 5

+2 A:

:%!awk -- '++c\%2'

alternatively

:%!awk -- 'c++\%2'

depending on which half you want to weed out.

Michael Krelin - hacker 2009-12-22 15:00:01

Umm, why not use the existing `NR` variable?

ephemient 2009-12-22 17:30:41

Right. Because I forgot about it. ;-) But actually, the "proper" variant will be even longer with NR. And there would be no two *nice-looking* counterparts.

Michael Krelin - hacker 2009-12-22 19:57:15

`:%!awk NR\%2` or `:%!awk 1-NR\%2`, as I posted in another comment. That's hardly longer.

ephemient 2009-12-22 19:58:41

`1-NR` is longer than `c++`. Yes, I know it's one character. Like I said — the real reason is that I forgot about it. Anyway, looks like people do not appreciate the beauty of awk here.

Michael Krelin - hacker 2009-12-22 20:21:28

And `NR` is shorter than `++c` :)

ephemient 2009-12-22 22:59:09

;-) True, that makes total the same. But like I said - I like the fearful symmetry of counterparts.

Michael Krelin - hacker 2009-12-22 23:04:29

Answer 6

+1 A:

You can use Vim's own search and substitute capabilities like so: Put your cursor at the first line, and type in normal mode:

:.,/fff/s/\n.*\(\n.*\)/\1/g

The .,/fff/ is the range for the substitution. It means "from this line to the line that matches the regex fff (in this case, the last line).
s/// is the substitute command. It looks for a regex and replaces every occurrence of it with a string. The g at the end means to repeat the substitution as long as the regex keeps being found.
The regex \n.*$\n.*$ matches a newline, then a whole line (.* matches any number of characters except for a newline), then another newline and another line. The parentheses $ and $ cause the expression inside them to be recorded, so we can use it later using \1.
\1 inserts the grouped newline and the line after it back, because we don't want the next line gone too - we just want the substitution mechanism to pass by it so we don't delete it in the next replacement.

This way you can control the range in which you want the deletion to take place, and you don't have to use any external tool.

Daniel Hershcovich 2009-12-22 15:02:38

Or `$` instead of `/fff/`, for end-of-file regardless of the file's contents.

ephemient 2009-12-22 17:32:20

Answer 7

A:

:map ^o ddj^o
^o

Here ^ stand for CTRL. Recursive macro to delete a line every two line. Choose well your first line and it's done.

Raoul Supercopter 2009-12-22 17:25:49

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Vim: how to delete every second row?

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