how to install matplotlib

$ pip install matplotlib

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* The following required packages can not be built:
* freetype, png
* Try installing freetype with `apt-get install
* libfreetype6-dev` and pkg-config with `apt-get
* install pkg-config`
* Try installing png with `apt-get install
* libpng12-dev` and pkg-config with `apt-get install
* pkg-config`

----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-LcxKFA/matplotlib/

$ sudo apt-get install libfreetype6-dev
$ sudo apt-get install pkg-config
$ pip install matplotlib