The easiest way to select multiple columns in Pandas is to pass a list into the standard square-bracket indexing scheme. For example, the expression df[[‘Col_1’, ‘Col_4, ‘Col_7’]] would access columns ‘Col_1’, ‘Col_4’, and ‘Col_7’. This is the most flexible and concise way for only a couple of columns. To learn about the best 3 ways …
Problem Formulation How to calculate the inverse of the normal cumulative distribution function (CDF) in Python? Method 1: scipy.stats.norm.ppf() In Excel, NORMSINV is the inverse of the CDF of the standard normal distribution. In Python’s SciPy library, the ppf() method of the scipy.stats.norm object is the percent point function, which is another name for the …
Python – Inverse of Normal Cumulative Distribution Function (CDF) Read More »
Broadcasting describes how NumPy automatically brings two arrays with different shapes to a compatible shape during arithmetic operations. Generally, the smaller array is “repeated” multiple times until both arrays have the same shape. Broadcasting is memory-efficient as it doesn’t actually copy the smaller array multiple times. Here’s a minimal example: Let’s have a more gentle …
Logistic regression is a popular algorithm for classification problems (despite its name indicating that it is a “regression” algorithm). It belongs to one of the most important algorithms in the machine learning space. Linear Regression Background Let’s review linear regression. Given the training data, we compute a line that fits this training data so that …
Problem Formulation Given a NumPy array consisting of Boolean values. How to convert it to an integer array? Convert each True value to integer 1, and Convet each False value to integer 0. Here’s an example Boolean array: What you want is the following integer array: Let’s examine some methods to accomplish this easily. Method …
How to Convert a Boolean Array to an Integer Array in Python? Read More »
Problem Formulation Given two NumPy arrays a and b. How to concatenate both? Method 1: np.concatenate() NumPy’s concatenate() method joins a sequence of arrays along an existing axis. The first couple of comma-separated array arguments are joined. If you use the axis argument, you can specify along which axis the arrays should be joined. For …
The double-frontslash // operator performs integer division and the single-frontslash / operator performs float division. An example for integer division is 40//11 = 3. An example for float division is 40/11 = 3.6363636363636362. A crucial lesson you need to master as a programmer is “division in Python”. What does it mean to divide in Python? …
If there is one clustering algorithm you need to know – whether you are a computer scientist, data scientist, or machine learning expert – it’s the K-Means algorithm. In this tutorial drawn from my book Python One-Liners, you’ll learn the general idea and when and how to use it in a single line of Python …
[Tutorial] K-Means Clustering with SKLearn in One Line Read More »
This article deals with signal processing. More precisely, it shows how to smooth a data set that presents some fluctuations, in order to obtain a resulting signal that is more understandable and easier to be analyzed. In order to smooth a data set, we need to use a filter, i.e. a mathematical procedure that allows …
Smoothing Your Data with the Savitzky-Golay Filter and Python Read More »
Scikit-learn has a library of transformers to preprocess a data set. These transformers clean, generate, reduce or expand the feature representation of the data set. These transformers provide the fit(), transform() and fit_transform() methods. The fit() method identifies and learns the model parameters from a training data set. For example, standard deviation and mean for …
Sklearn fit() vs transform() vs fit_transform() – What’s the Difference? Read More »
Problem Formulation Given an image stored at image.jpeg, a target width and height in pixels, and a target starting point (upper-left) x and y in the coordinate system. How to crop the given image in Python OpenCV so that the resulting image has width * height size? Here’s an example of how the original image …
You’d like to add text to your plot, perhaps to explain an outlier or label points. Matplotlib‘s text method allows you to add text as specified coordinates. But if you want the text to refer to a particular point, but you don’t want the text centered on that point? Often you’ll want the text slightly …