Ubuntu – top / htop; group process by command

From man htop:

INTERACTIVE COMMANDS

Space Tag or untag a process. Commands that can operate on multiple processes, like "kill", will then apply over the list of tagged processes, instead of the currently highlighted one.

U Untag all processes (remove all tags added with the Space key).

F9, k "Kill" process: sends a signal which is selected in a menu, to one or a group of processes. If processes were tagged, sends the signal to all tagged processes. If none is tagged, sends to the currently selected process.

Not quite the answer you were looking for, but close. You can also eliminate process groups or children with kill, see:

https://stackoverflow.com/questions/392022/best-way-to-kill-all-child-processes

You can simply use grep:

NAME
       grep, egrep, fgrep, rgrep - print lines matching a pattern

SYNOPSIS
       grep [OPTIONS] PATTERN [FILE...]
       grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]

DESCRIPTION
       grep  searches  the  named  input  FILEs (or standard input if no files are named, or if a single
       hyphen-minus (-) is given as file name) for lines containing a match to the  given  PATTERN.   By
       default, grep prints the matching lines.

Run following command to get output which you want (ex-chrome):

top | grep chrome

Here we are using grep with pipelines | so top & grep run parallel ; top output given to grep (as input) and grep chrome filters matching lines chrome until top stopped.