This extension lets you view files through a filter specified by a text string or a regular expression. Hidden lines that don't match the filter can be easily hidden or revealed.
This tool is intended primary as a log viewer to make browsing through large text files manageable and more convenient.
Usage
How to Start Condensing
When inside a text editor - press Ctrl+' (⌘').
Alternatively, press Ctrl+Shift+P (⇧⌘P), then enter "Condense start".
Condenser Dialog box with buttons (expand all), (collapse all), and (stop condensing) is shown now at the text editor's top.
How to Set a Filter
Select some text inside an editor, then press Ctrl+' (⌘'); selected text is automatically applied as a filter.
When in Condenser Dialog - type text and watch the editor's contents change.
When in Condenser Dialog - use Up / Down keys to browse through history.
Pressing Enter inside Condenser Dialog saves the current filter in history - pressing Esc does not.
How to Hide and Reveal Text
Clicking the folding icon on the gutter between a line's number and its text, hides or reveals folded text.
Click on a line inside a text editor, then press Ctrl+Shift+] (⌥⌘]) to expand the fold under that line or, alternatively, press Ctrl+Shift+[ (⌥⌘[) to collapse it.
When in Condenser Dialog - click the button to expand the entire file or the button to collapse it.
How to Stop Condensing
Press Ctrl+Shift+' (⇧⌘').
When in Condenser Dialog - click the button or, alternatively, clear the text and then press Enter.
Press Ctrl+Shift+P (⇧⌘P), then enter "Condense stop".
Known Issues
As Log Condenser does not check file types, folding may get confused when applied to structured content such as JSON, HTML, JavaScript etc, i.e. files for which folding is already provided by a language support package.
(expand all), 
(collapse all), and 
(stop condensing) is shown now at the text editor's top.