Unmet dependencies installing R 3.6.2 on Ubuntu 18.14 LTS - r

Question

I use 18.04.4 LTS (Bionic Beaver)
I wanted to upgrade my R version from 3.4.4 to 3.6.2, but now I have no R at all.
here are my actions:
1 step:
sudo apt update
sudo apt-get upgrade
sudo apt-get dist-upgrade
2 step:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E298A3A825C0D65DFD57CBB651716619E084DAB9
3 step:
sudo add-apt-repository 'deb https://cloud.r-project.org/bin/linux/ubuntu bionic-cran35/'
return:
Hit:1 http://ua.archive.ubuntu.com/ubuntu bionic InRelease
Hit:2 http://ua.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:3 http://ua.archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit:4 http://cran.rstudio.com/bin/linux/ubuntu bionic-cran35/ InRelease
Hit:5 http://ppa.launchpad.net/ondrej/php/ubuntu bionic InRelease
Hit:6 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:7 https://cloud.r-project.org/bin/linux/ubuntu xenial-cran35/ InRelease
Hit:8 https://cloud.r-project.org/bin/linux/ubuntu disco-cran35/ InRelease
Hit:9 https://cloud.r-project.org/bin/linux/ubuntu bionic-cran35/ InRelease
Reading package lists... Done
4 step:
sudo apt update
sudo apt install r-base
return:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
r-base : Depends: r-base-core (>= 3.6.2-1xenial) but it is not going to be installed
Depends: r-recommended (= 3.6.2-1xenial) but it is not going to be installed
Recommends: r-base-html but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
then I try:
R --version
return:
Command 'R' not found, but can be installed with:
sudo apt install r-base-core
I try:
sudo apt install r-base-core
The following packages have unmet dependencies:
r-base-core : Depends: libreadline6 (>= 6.0) but it is not
installable
Recommends: r-recommended but it is not going to be
installed
Recommends: r-base-dev but it is not going to be
installed
E: Unable to correct problems, you have held broken packages.

Answer 1

You can try two things:
As you already appear to have installed, just to sudo apt-get dist-upgrade. It will list candidate upgrades, you can still back out. Advantage: it resolved interdependent upgrades for you.
Continue what you did but list the affected packages, i.e. sudo apt-get install r-base r-recommended r-base-hmtml. This will work, but may requires several iterative steps.

Answer 2

I took a look at the etc/apt/sources.list file and realised that I had the same repository repeated. I deleted two lines and the problem was solved.