I launch a docker container from an image with the following command:
$ docker run -d myimage /bin/bash -c "mycommand"
When "mycommand" is finished, the container is stopped (I suppose it is stopped), but it is not deleted, because I can see it with this command:
$ docker ps -a
Is there any way to restart this container with the same parameters and keep data generated by mycommand?
Yes, when the CMD task finishes its execution (either normally or because of an error, including "the command you're trying to run is a bad command") the container stops.
You can start a stopped container by using:
docker start container_name
If you want to see the output of your command then you should add -ai options, where "a" tells docker to attach the container's stdout and stderr to your current terminal, and "i" tells docker to attach stdin, too.
docker start -ai container_name
(There is also a restart command, but that is only for restarting a still running container, not a stopped container)