Miniconda is a minimal implementation of Anaconda that only contains the conda package manager and Python. These Docker images build upon Ubuntu 17.04, as oppose to the official continuumio images which use Debian. Once Miniconda is installed, you can use the conda command to install any other packages, create environments, etc.
$ conda install numpy
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$ conda install -c bioconda samtools
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$ conda create -n py3k anaconda python=3
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Read more about Miniconda here. This README.md file is slightly modified version of information from the official page.