The Mindful Programmer

Plotting a time series heat map with Pandas

Joni — Sun, 17 Nov 2019 16:53:37 +0000

Heat maps communicate succinctly how the distribution of a value evolves over time. Performance metrics like latency or API response time often have a complicated multimodal distributions, and summarizing them in single values like mean or 90th percentile for a visualization makes many interesting events invisible. You need to look at histograms to see the …

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Get binary search right the first time

Joni — Mon, 28 Nov 2016 23:43:58 +0000

Binary search is one of the first algorithms that people learn. The idea is wonderfully simple: Yet it’s so easy to get the details wrong. In fact, nearly all binary searches are broken. If you set out to write a binary search, you would probably start out with an outline like this: Then you stop …

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Efficient and accurate rolling standard deviation

Joni — Tue, 06 May 2014 18:27:50 +0000

The usual algorithms for computing variance and standard deviation work on the full data set. What if you have a time series and want the standard deviation for a moving window? You could do the computation from fresh every time the window is advanced, but surely there’s a better way. Let’s denote the data by …

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The Number With Negative Absolute Value

Joni — Sun, 20 Apr 2014 05:00:46 +0000

As you know, computers internally work only with ones and zeros, and everything is represented in some way using these “bits.” Using M bits you can encode 2M different values. Let’s say you’re interested in encoding the signed integers …, -1, 0, 1, 2, …. To make things simple, let’s use a fixed number of …

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Verify and generate IBAN in PHP and MySQL

Joni — Sun, 13 Apr 2014 04:00:38 +0000

With the introduction of SEPA, the use of IBAN is now mandatory for all bank transactions in the Euro zone. This forces almost everyone to migrate their data, replacing national bank account numbers with IBANs. Fortunately this is a fairly simple task: to get the IBAN for an existing account, take the two-character country code, …

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