Xarray Tips and Tricks¶

Build a multi-file dataset from an OpenDAP server¶

One thing we love about xarray is the open_mfdataset function, which combines many netCDF files into a single xarray Dataset.

But what if the files are stored on a remote server and accessed over OpenDAP. An example can be found in NOAA's NCEP Reanalysis catalog.

Xarray for multidimensional gridded data¶

In last week's lecture, we saw how Pandas provided a way to keep track of additional "metadata" surrounding tabular datasets, including "indexes" for each row and labels for each column. These features, together with Pandas' many useful routines for all kinds of data munging and analysis, have made Pandas one of the most popular python packages in the world.

Pandas: Groupby¶

groupby is an amazingly powerful function in pandas. But it is also complicated to use and understand. The point of this lesson is to make you feel confident in using groupby and its cousins, resample and rolling.

These notes are loosely based on the Pandas GroupBy Documentation.

Imports:

Pandas¶

Pandas is a an open source library providing high-performance, easy-to-use data structures and data analysis tools. Pandas is particularly suited to the analysis of tabular data, i.e. data that can can go into a table. In other words, if you can imagine the data in an Excel spreadsheet, then Pandas is the tool for the job.

More Matplotlib¶

Matplotlib is the dominant plotting / visualization package in python. It is important to learn to use it well. In the last lecture, we saw some basic examples in the context of learning numpy. This week, we dive much deeper. The goal is to understand how matplotlib represents figures internally.

Numpy and Matplotlib¶

These are two of the most fundamental parts of the scientific python "ecosystem". Most everything else is built on top of them.

Python Functions, Classes, and Modules¶

For longer and more complex tasks, it is important to organize your code into reuseable elements. For example, if you find yourself cutting and pasting the same or similar lines of code over and over, you probably need to define a function to encapsulate that code and make it reusable. An important principle in programming in DRY more ...

Core Python Language¶

Mostly copied from the official python tutorial

Invoking Python¶

There are three main ways to use python.

1. By running a python file, e.g. python myscript.py
2. Through an interactive console (python interpreter or ipython shell)
3. In an interactive iPython notebook

We will be using the iPython notebook.

Python Versions¶

There are two versions of the python language out there: python 2 and python 3. Python 2 is more common in the wild but is depracated. The community is moving to python 3. As new python learners, you should learn python 3. But it is important to be aware that python 2 exists. It is possible that a package you want to use is only supported in python 2. In general, it is pretty easy to switch between then.