Sampling Data Lake Data

Alex Whittles shows how to use U-SQL to sample data to read in Power BI:

The answer is sampling, we don’t bring in 100% of the data, but maybe 10%, or 1%, or even 0.01%, it depends how much you need to reduce your dataset. It is however critical to know how to sample data correctly in order to maintain a level of accuracy of data in your reports.

Option 1: Take the top x rows of data
Don’t do it. Ever. Just no.
What if the source data you’ve been given is pre-sorted by product or region, you’d end up with only data from products starting with ‘a’, which would give you some wildly unpredictable results.

Option 2: Take a random % sample
Now we’re talking. This option will take, for example 1 in every 100 rows of data, so it’s picking up an even distribution of data throughout the dataset. This seems a much better option, so how do we do it?

Read on for a couple of sampling methods.

Related Posts

Power BI Helper 3.0

Reza Rad has a new version of Power BI Helper out: It is a pleasure to announce the newest version of Power BI helper, version 3.0 July 2018 with the great feature of exporting model documentation. The documentation part of the insight from Power BI Helper has been always in our backlog, but haven’t had […]

Read More

Data Lakes And Data Swamps

Randolph West talks about data lakes: Internet companies including search engines (Google, Bing), social media companies (Facebook, Twitter), and email providers (Yahoo!, Outlook.com) are managing data stores measured in petabytes. On a daily basis these organizations handle all sorts of structured and unstructured data. Assuming they put all their data in one repository, that could […]

Read More

Categories

January 2017
MTWTFSS
« Dec Feb »
 1
2345678
9101112131415
16171819202122
23242526272829
3031