DataFrames.jl release 0.21

DataFrames.jl version 0.21 was a major release that introduced a number of significant changes to DataFrames.jl API. The list is long, so I briefly summarize here he most significant things in terms of functionality:

• we now allow to select columns using strings (selection using Symbols is still allowed);
• a completely new design of API for working with columns of a data frame or grouped data frame, covered by select/select!, transform/transform!, and combine functions; it is consistent (so you learn it once and reuse everywhere), more flexible, and has a better performance than the old one; in particular two wrappers ByRow and AsTable have been added to API;
• major enhancements to push! and append!, which allow an easy way to digest heterogeneous data (varying element types, varying column sets) into a data frame;
• GroupedDataFrame now supports a fast lookup by grouping columns (so making a GroupedDataFrame can be now seen as adding an index to a data frame)
• filter/filter! are now fast using Pair-interface;
• rules for pseudo-broadcasting (spreading single observations across multiple rows) have been established and are consistently applied in all methods that allow this operation.

All these changes combined mean that now all operations on data frames can be expressed via function chaining (and you have a full control if you want to make copies or perform operations in-place). There are many users who like this style of expressing transformations made on data. If you want to go this way, then probably you should consider learning one of the packages that makes it easier to work with |> operator. There are many excellent alternatives in the Julia ecosystem. Let me mention two Pipe.jl (easier) and Underscores.jl (more powerful, but harder to master).

After the release I got several questions about showing how things work in practice. Therefore in this post I list tutorials that are currently available and have been updated to show how DataFrames.jl v0.21 works.

In the Part II post (that I plan to prepare next week) I will show some new material that was prepared under DataFrames.jl v0.21.

Tutorials for release 0.21

There are four sources of information about the functionality of DataFrames.jl 0.21 that you can check out (and I maintain them so that they should be up to date):

1. An official DataFrames.jl Manual.
2. A notebook-based DataFrames.jl Tutorial.