diff --git a/machine_learning/data_transformations.py b/machine_learning/data_transformations.py new file mode 100644 index 000000000..9e0d747e9 --- /dev/null +++ b/machine_learning/data_transformations.py @@ -0,0 +1,62 @@ +""" +Normalization Wikipedia: https://en.wikipedia.org/wiki/Normalization +Normalization is the process of converting numerical data to a standard range of values. +This range is typically between [0, 1] or [-1, 1]. The equation for normalization is +x_norm = (x - x_min)/(x_max - x_min) where x_norm is the normalized value, x is the +value, x_min is the minimum value within the column or list of data, and x_max is the +maximum value within the column or list of data. Normalization is used to speed up the +training of data and put all of the data on a similar scale. This is useful because +variance in the range of values of a dataset can heavily impact optimization +(particularly Gradient Descent). + +Standardization Wikipedia: https://en.wikipedia.org/wiki/Standardization +Standardization is the process of converting numerical data to a normally distributed +range of values. This range will have a mean of 0 and standard deviation of 1. This is +also known as z-score normalization. The equation for standardization is +x_std = (x - mu)/(sigma) where mu is the mean of the column or list of values and sigma +is the standard deviation of the column or list of values. + +Choosing between Normalization & Standardization is more of an art of a science, but it +is often recommended to run experiments with both to see which performs better. +Additionally, a few rules of thumb are: + 1. gaussian (normal) distributions work better with standardization + 2. non-gaussian (non-normal) distributions work better with normalization + 3. If a column or list of values has extreme values / outliers, use standardization +""" +from statistics import mean, stdev + + +def normalization(data: list, ndigits: int = 3) -> list: + """ + Returns a normalized list of values + @params: data, a list of values to normalize + @returns: a list of normalized values (rounded to ndigits decimal places) + @examples: + >>> normalization([2, 7, 10, 20, 30, 50]) + [0.0, 0.104, 0.167, 0.375, 0.583, 1.0] + >>> normalization([5, 10, 15, 20, 25]) + [0.0, 0.25, 0.5, 0.75, 1.0] + """ + # variables for calculation + x_min = min(data) + x_max = max(data) + # normalize data + return [round((x - x_min) / (x_max - x_min), ndigits) for x in data] + + +def standardization(data: list, ndigits: int = 3) -> list: + """ + Returns a standardized list of values + @params: data, a list of values to standardize + @returns: a list of standardized values (rounded to ndigits decimal places) + @examples: + >>> standardization([2, 7, 10, 20, 30, 50]) + [-0.999, -0.719, -0.551, 0.009, 0.57, 1.69] + >>> standardization([5, 10, 15, 20, 25]) + [-1.265, -0.632, 0.0, 0.632, 1.265] + """ + # variables for calculation + mu = mean(data) + sigma = stdev(data) + # standardize data + return [round((x - mu) / (sigma), ndigits) for x in data]