Re: Collapse out all lines not matching "/pattern"?

On 7/13/25 15:24, Joseph Wulf wrote:
> In regular/normal vim editing, is there a method to collapse out of
> view all lines NOT matching "/pattern"?

Joe,

Vim folding can be used to hide lines from view (see `:help
folding`).  I've got a few functions and commands in my vimrc
for this; `:FoldSearch pattern` shows lines matching `pattern`
and folds away everything else.  Here are my notes about using
these commands:

```
Folding by regular expression                          
*notes_folding_regex*

To fold away lines that match a regex, use the custom command :Fold: >
    :Fold regex         ; lines matching regex are hidden
    :Fold               ; use last search pattern (@/) for regex

Use the custom command :FoldSearch to search for lines matching a regex and
fold away everything else: >
    :FoldSearch regex   ; show lines matching regex, and fold away all else
    :FoldSearch         ; use last search pattern (@/) for regex

With :FoldSearch, increasing the 'foldlevel' to 1 will show one line of
context around all matches.

To fold away comments and blank lines, use this custom command: >
    :FoldComments

------------------------------------------------------------------------------
QuickFix entry folding                                 
*notes_quickfix_folding*

To group lines of QuickFix output together by files or by directories,
use one
of the following commands when a QuickFix or Location List window is
focused:

                                  *FoldQuickFixFiles*
                                  *FoldQuickFixDirs*
    :[count] FoldQuickFixFiles
    :[count] FoldQuickFixDirs

When [count] is 0 (the default), the folds will start closed; when
[count] is 1,
the folds will start open.

When a QuickFix or Location List window is opened, :1FoldQuickFixFiles is
applied by :SetupQuickFix, such that the folds start open.  Use standard Vim
shortcut keys within the QuickFix or Location List window to change folding
levels:

    zr    Reduce amount of folding
    zR    Reduce amount of folding fully (no folding remaining)
    zm    More folding
    zM    More folding (fully folded)
    zo    Open a fold
    zc    Close a fold

In Gvim, you may also click on the symbols in the left margin of the
QuickFix
or Location List window to toggle individual folds.
```

Below are the functions and commands from vimrc.

```vim
" =============================================================
" Folding
" =============================================================

function! FoldShowExpr()
    let maxLevel = 2
    let level = 0
    while level < maxLevel
        if getline(v:lnum - level) =~ @/
            break
        endif
        if level != 0 && (getline(v:lnum + level) =~ @/)
            break
        endif
        let level = level + 1
    endwhile
    return level
endfunction

function! FoldHideExpr()
    return (getline(v:lnum) =~ @/) ? 1 : 0
endfunction

function! FoldRegex(foldExprFunc, regex)
    if a:regex != ""
        let @/=a:regex
        call histadd("search", a:regex)
    endif
    let &l:foldexpr = a:foldExprFunc . '()'
    setlocal foldmethod=expr
    setlocal foldlevel=0
    setlocal foldcolumn=0
    setlocal foldminlines=0
    setlocal foldenable

    " Return to manual folding now that folds have been applied.
    setlocal foldmethod=manual
endfunction

" Search (and "show") regex; fold everything else.
command! -nargs=? FoldSearch    call FoldRegex('FoldShowExpr', <q-args>)

" Fold matching lines ("hide" the matches).
command! -nargs=? Fold          call FoldRegex('FoldHideExpr', <q-args>)

" Fold away comment lines (including blank lines).
" TODO: Extend for more than just shell comments.
command! -nargs=? FoldComments  Fold ^\s*#\|^\s*$

" 'foldexpr' for extracting folding information from QuickFix buffer.
" pattern - used to extract portion of QuickFix path from line.
function! FoldQuickFixPatternFoldExpr(pattern)
    let thisLine = getline(v:lnum)
    let nextLine = getline(v:lnum + 1)
    let thisKey = matchstr(thisLine, a:pattern)
    let nextKey = matchstr(nextLine, a:pattern)
    if thisKey != nextKey
        return '<1'
    else
        return '1'
    endif
endfunction

function! FoldQuickFixDirsFoldExpr()
    return FoldQuickFixPatternFoldExpr('\v^.*[/\\]')
endfunction

" Fold QuickFix window entries by directory.
"   level - initial foldlevel (0 => fold everything, 1 => expand all folds)
function! FoldQuickFixDirs(level)
    let &l:foldlevel = a:level
    setlocal foldcolumn=1
    setlocal foldmethod=expr
    setlocal foldexpr=FoldQuickFixDirsFoldExpr()
endfunction
command! -count=0 FoldQuickFixDirs  call FoldQuickFixDirs(<count>)

function! FoldQuickFixFilesFoldExpr()
    return FoldQuickFixPatternFoldExpr('\v^[^|]*')
endfunction

" Fold QuickFix window entries by filename.
"   level - initial foldlevel (0 => fold everything, 1 => expand all folds)
function! FoldQuickFixFiles(level)
    let &l:foldlevel = a:level
    setlocal foldcolumn=1
    setlocal foldmethod=expr
    setlocal foldexpr=FoldQuickFixFilesFoldExpr()
    setlocal foldenable
endfunction
command! -count=0 FoldQuickFixFiles  call FoldQuickFixFiles(<count>)
```

Michael Henry

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