The feature is available in commercial UltraEdit https://www.ultraedit.com/

-anandcoral (December 02, 2019, 10:55 AM)

Thanks. I'm trying it now in the UE trial. This comes closest to my OP wishlist so far. The hide lines feature for any type of textfile must first be enabled in the settings. After that we doubletap control+F to get "Find and Replace". Click filter checkbox, type a string and hit Enter. Not too slow. Line hiding looks like regular code folding. We can filter in or out and regex filter.

Two drawbacks:
- Filtering/unfiltering could be quicker and fewer steps. I see no direct hotkey to toggle unhide for all the previously hidden lines. But it can be done in two steps: Control+A to select all and then unhide through hotkey or command palette. The filtering command also shares UI with the find and replace. This means that we have to check/uncheck the filter checkbox in Find and Replace window when switching from filtering mode to find and replace mode. If would be quicker if they were separate popup windows.
- UE can split view the text. But any line filtering is synced when the second view is focused. So we can't shift back and forth between views and keep only one of them filtered.

But maybe there are workarounds to these issues through settings or scripts. I'll play some more with it.

Screenshot from UE's Find and Replace window


Screenshot of UE with split view after line filtering. Notice that both views are filtered.

but since you are interested in free one, this will not do.

-anandcoral (December 02, 2019, 10:55 AM)

Free isn't required. But as a first step I mostly just want to test drive this kind of feature for a while, to figure out if and when it is most useful compared to regular find and replace and other methods.

My hunch is that the feature would be most useful, and that I'd find more use for it, if the filter/unfilter action is very quick. Ideally a keyboard shortcut for a small searchbox (not with a lot of checkboxes and other functionality) and then filter lines as you type. Similarly one step shortcuts to unfilter all lines, unfilter this line, and so on.

I distinctly remember using Notepad++ to apply a filter to a text file, for the purpose of hiding away 80% of it's content and doing manual changes on the content that still was shown.

-Shades (November 30, 2019, 06:04 AM)

Thanks. I see the "Hide Lines" (alt+H) command in Notepad++ menu View. But no "unhide" keyboard shortcut, though clicking the green hidden lines markers in the linenumber column works. Will try the TextFX Viz next.

I'm also tinkering on a small AutoHotkey test script with two views where one is filterable. The two only sync on save yet, I'll try sync as you type next.

Some thoughts from playing with it so far. To be most useful I think this kind of linefilter/accordion tool will need a few extra features:
- Linenumbers is a must
- shortcuts to unhide +1 lines line above or below current position (and +5, and +N)
- smart ways to toggle between edits in the filtered view affecting only visible lines vs all content. E.g. if line 2 is hidden and we select from line 1 to 3, should Delete also remove line 2? Or only 1 and 3?; Ditto find and replace.
- negative filter syntax (e.g. toggle all code comment lines off)
- filtering lines could be very handy together with multi caret editing. You want to rename a variable name everywhere in a long code document. First filter lines with the current variable name. Then hit shortcut to start multi caret editing at the start of the filter string on each visible line. Same end result as find and replace on the filtered view lines, but different visual response and easier to backtrack and adjust the new name while typing it.