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Advanced Data Reshaping in Python and R

This note is a simple data wrangling example worked using both the Python data_algebra package and the R cdata package. Both of these packages make data wrangling easy through he use of coordinatized data concepts (relying heavily on Codd’s “rule of access”).

The advantages of data_algebra and cdata are:

  • The user specifies their desired transform declaratively by example and in data. What one does is: work an example, and then write down what you want (we have a tutorial on this here).
  • The transform systems can print what a transform is going to do. This makes reasoning about data transforms much easier.
  • The transforms, as they themselves are written as data, can be easily shared between systems (such as R and Python).

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Introducing data_algebra

This article introduces the data_algebra project: a data processing tool family available in R and Python. These tools are designed to transform data either in-memory or on remote databases.

In particular we will discuss the Python implementation (also called data_algebra) and its relation to the mature R implementations (rquery and rqdatatable).

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Posted on Categories data science, Exciting Techniques, Practical Data Science, Pragmatic Data Science, TutorialsTags , ,

Data Layout Exercises

John Mount, Nina Zumel; Win-Vector LLC 2019-04-27

In this note we will use five real life examples to demonstrate data layout transforms using the cdata R package. The examples for this note are all demo-examples from tidyr:demo/ (current when we shared this note on 2019-04-27, removed 2019-04-28), and are mostly based on questions posted to StackOverflow. They represent a good cross-section of data layout problems, so they are a good set of examples or exercises to work through.

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Posted on Categories Coding, Practical Data Science, Pragmatic Data Science, TutorialsTags , , 4 Comments on Controlling Data Layout With cdata

Controlling Data Layout With cdata

Here is an example how easy it is to use cdata to re-layout your data.

Tim Morris recently tweeted the following problem (corrected).

Please will you take pity on me #rstats folks?
I only want to reshape two variables x & y from wide to long!

Starting with:
    d xa xb ya yb
    1  1  3  6  8
    2  2  4  7  9

How can I get to:
    id t x y
    1  a 1 6
    1  b 3 8
    2  a 2 7
    2  b 4 9
    
In Stata it's:
 . reshape long x y, i(id) j(t) string
In R, it's:
 . an hour of cursing followed by a desperate tweet 👆

Thanks for any help!

PS – I can make reshape() or gather() work when I have just x or just y.

This is not to make fun of Tim Morris: the above should be easy. Using diagrams and slowing down the data transform into small steps makes the process very easy.

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The blocks and rows theory of data shaping

We have our latest note on the theory of data wrangling up here. It discusses the roles of “block records” and “row records” in the cdata data transform tool. With that and the theory of how to design transforms, we think we have a pretty complete description of the system.

Rowrecs to blocks

Posted on Categories Coding, data science, Programming, TutorialsTags , , , , 15 Comments on Using a Column as a Column Index

Using a Column as a Column Index

We recently saw a great recurring R question: “how do you use one column to choose a different value for each row?” That is: how do you use a column as an index? Please read on for some idiomatic base R, data.table, and dplyr solutions.

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Wanted: cdata Test Pilots

I need a few volunteers to please “test pilot” the development version of the R package cdata, please.

Jackie Cochran at 1938 Bendix Race
Jacqueline Cochran: at the time of her death, no other pilot held more speed, distance, or altitude records in aviation history than Cochran.

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Posted on Categories Computer Science, data science, Practical Data Science, Pragmatic Data Science, Pragmatic Machine Learning, ProgrammingTags , , , , , , 3 Comments on rquery: Fast Data Manipulation in R

rquery: Fast Data Manipulation in R

Win-Vector LLC recently announced the rquery R package, an operator based query generator.

In this note I want to share some exciting and favorable initial rquery benchmark timings.

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Posted on Categories Administrativia, Opinion, Pragmatic Data Science, Pragmatic Machine Learning, Programming, StatisticsTags , , , , , , , , 4 Comments on Getting started with seplyr

Getting started with seplyr

A big “thank you!!!” to Microsoft for hosting our new introduction to seplyr. If you are working R and big data I think the seplyr package can be a valuable tool.


Safety
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Posted on Categories Pragmatic Data Science, Pragmatic Machine Learning, Programming, Statistics, TutorialsTags , , , , , , ,

Data Wrangling at Scale

Just wrote a new R article: “Data Wrangling at Scale” (using Dirk Eddelbuettel’s tint template).

Fd

Please check it out.