Quite often I come across transformations that are applicable to several scenarios. So created this reusable Python class that leverages PySpark capabilities to apply common transformation to a dataframe or a subset of columns in a dataframe. The code is in GitHub – bennyaustin/pyspark-utils. There is also an extensive function reference and usage document to go with it. Feel free to use, extend, request features and contribute.Continue reading
At the moment SQL MERGE operation is not available in Azure Synapse Analytics. However, it is possible to implement this feature using Azure Synapse Analytics connector in Databricks with some PySpark code.Continue reading
PySpark has built-in functions to shift time between time zones. Just need to follow a simple rule. It goes like this. First convert the timestamp from origin time zone to UTC which is a point of reference. Then convert the timestamp from UTC to the required time zone. In this way there is no need to maintain lookup tables and its a generic method to convert time between time zones even for the ones that require daylight savings offset.Continue reading
Parquet is my preferred format for storing files in data lake. Parquet’s columnar storage and compression makes it very efficient for in-memory processing tasks like Spark/Databricks notebooks while saving cost on storage. Parquet also supports almost all encoding schemes out there. Perhaps the coolest thing in Parquet is unlike CSV there is no such thing as column/row separator. So there is no need to escape those characters if they are part of data.
Azure SQL Data Warehouse supports Parquet data format for External (PolyBase) tables. External tables reference the underlying storage blobs and gives an option to query the data lake using SQL. In fact this is recommended in Microsoft’s reference architecture. With some Parquet files this error gets thrown when the External Table is queried
HdfsBridge::recordReaderFillBuffer – Unexpected error encountered filling record reader buffer: IllegalArgumentException: Must be 12 bytes
In the absence of clear exception message it took a while to figure this out. This error usually happens on a Timestamp column specifically when the data is in yyyy/MM/dd hh:mm:ss format. For some reason SQL Data Warehouse expects the Timestamp data to be in yyyy-MM-dd hh:mm:ss format. Changing the date separator from / to – resolved this issue, although it must be mentioned the underlying file is a perfectly valid Parquet file.
A brief retrospective of my submission for Kaggle data science competition that predicts the gender and age group of a smartphone user based on their usage pattern.Continue reading
Slowly Changing Dimension (SCD) is great for tracking historical changes to dimension attributes. SCDs have evolved over the years and besides the conventional type 1 (update), type 2 (add row) and type 3 (add column), now there are extensions up to type 7 including type 0. Almost every DW/BI project has at least few type 2 dimensions where a change to an attribute causes the current dimension record to be end dated and creates a new record with the new value.Continue Reading
Time Series is the historical representation of data points collected at periodic intervals of time. Statistical tools like R use forecasting models to analyse historical time series data to predict future values with reasonable accuracy. In this post I will be using R time series to forecast the exchange rate of Australian dollar using daily closing rate of the dollar collected over a period of two years.Continue reading
Decision tree is a data mining model that graphically represents the parameters that are most likely to influence the outcome and the extent of influence. The output is similar to a tree/flowchart with nodes, branches and leaves. The nodes represent the parameters, the branches represent the classification question/decision and the leaves represent the outcome (Screen Capture 1). Internally, decision tree algorithm performs a recursive classification on the input dataset and assigns each record to a segment of the tree where it fits closest.
There are several packages in R that generate decision trees. For this post, I am using the ctree() function available in party package. The data I am using as input is energy rating of household air conditioners.
Box plot is an effective way to visualize the distribution of your data.It only takes a few lines of code in R to come up with a basic box plot.Continue Reading