Gap Statistic: Dynamically Get The Suggested Clusters in The Data

Python implementation of the Gap Statistic

Purpose

Dynamically identify the suggested number of clusters in a data-set using the gap statistic.

Full example available in a notebook HERE

Install:

Bleeding edge:

pip install git+git://github.com/milesgranger/gap_statistic.git

PyPi:

pip install --upgrade gap-stat

With Rust extension:

pip install --upgrade gap-stat[rust]

Uninstall:

pip uninstall gap-stat

Methodology:

This package provides several methods to assist in choosing the optimal number of clusters for a given dataset, based on the Gap method presented in "Estimating the number of clusters in a data set via the gap statistic" (Tibshirani et al.).

The methods implemented can cluster a given dataset using a range of provided k values, and provide you with statistics that can help in choosing the right number of clusters for your dataset. Three possible methods are:

Taking the k maximizing the Gap value, which is calculated for each k. This, however, might not always be possible, as for many datasets this value is monotonically increasing or decreasing.
Taking the smallest k such that Gap(k) >= Gap(k+1) - s(k+1). This is the method suggested in Tibshirani et al. (consult the paper for details). The measure diff = Gap(k) - Gap(k+1) + s(k+1) is calculated for each k; the parallel here, then, is to take the smallest k for which diff is positive. Note that in some cases this can be true for the entire range of k.
Taking the k maximizing the Gap* value, an alternative measure suggested in "A comparison of Gap statistic definitions with and with-out logarithm function" by Mohajer, Englmeier and Schmid. The authors claim this measure avoids the over-estimation of the number of clusters from which the original Gap statistics suffers, and can also suggest an optimal value for k for cases in which Gap cannot. They do warn, however, that the original Gap statistic performs better than Gap* in the case of overlapped clusters, due to its tendency to overestimate the number of clusters.

Note that none of the above methods is guaranteed to find an optimal value for k, and that they often contradict one another. Rather, they can provide more information on which to base your choice of k, which should take numerous other factors into account

Use:

First, construct an OptimalK object. Optional intialization parameters are:

n_jobs - Splits computation into this number of parallel jobs. Requires choosing a parallel backend.
parallel_backend - Possible values are joblib, rust or multiprocessing for the built-in Python backend. If parallel_backend == 'rust' it will use all cores.
clusterer - Takes a custom clusterer function to be used when clustering. See the example notebook for more details.
clusterer_kwargs - Any keyword arguments to be forwarded to the custom clusterer function on each call.

An example intialization:

optimalK = OptimalK(n_jobs=4, parallel_backend='joblib')

After the object is created, it can be called like a function, and provided with a dataset for which the optimal K is found and returned. Parameters are:

X - A pandas dataframe or numpy array of data points of shape (n_samples, n_features).
n_refs - The number of random reference data sets to use as inertia reference to actual data. Optional.
cluster_array - A 1-dimensional iterable of integers; each representing n_clusters to try on the data. Optional.

For example:

import numpy as np
n_clusters = optimalK(X, cluster_array=np.arange(1, 15))

After performing the search procedure, a DataFrame of gap values and other usefull statistics for each passed cluster count is now available as the gap_df attributre of the OptimalK object:

optimalK.gap_df.head()

The columns of the dataframe are:

n_clusters - The number of clusters for which the statistics in this row were calculated.
gap_value - The Gap value for this n.
gap* - The Gap* value for this n.
ref_dispersion_std - The standard deviation of the reference distributions for this n.
sk - The standard error of the Gap statistic for this n.
sk* - The standard error of the Gap* statistic for this n.
diff - The diff value for this n (see the methodology section for details).
diff* - The diff* value for this n (corresponding to the diff value for Gap*).

Additionally, the relation between the above measures and the number of clusters can be plotted by calling the OptimalK.plot_results() method (meant to be used inside a Jupyter Notebook or a similar IPython-based notebook), which prints four plots:

A plot of the Gap value versus n, the number of clusters.
A plot of diff versus n.
A plot of the Gap* value versus n, the number of clusters.
A plot of the diff* value versus n.

Download Details:
Author: milesgranger
Source Code: https://github.com/milesgranger/gap_statistic
License: View license

#rust #machine-learning #python #statistics

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Gap Statistic: Dynamically Get The Suggested Clusters in The Data

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How to Automate Excel with Python | Python Excel Tutorial (OpenPyXL)

How to Automate Excel with Python

In this article, We will show how we can use python to automate Excel . A useful Python library is Openpyxl which we will learn to do Excel Automation

What is OPENPYXL

Openpyxl is a Python library that is used to read from an Excel file or write to an Excel file. Data scientists use Openpyxl for data analysis, data copying, data mining, drawing charts, styling sheets, adding formulas, and more.

Workbook: A spreadsheet is represented as a workbook in openpyxl. A workbook consists of one or more sheets.

Sheet: A sheet is a single page composed of cells for organizing data.

Cell: The intersection of a row and a column is called a cell. Usually represented by A1, B5, etc.

Row: A row is a horizontal line represented by a number (1,2, etc.).

Column: A column is a vertical line represented by a capital letter (A, B, etc.).

Openpyxl can be installed using the pip command and it is recommended to install it in a virtual environment.

pip install openpyxl

CREATE A NEW WORKBOOK

We start by creating a new spreadsheet, which is called a workbook in Openpyxl. We import the workbook module from Openpyxl and use the function Workbook() which creates a new workbook.

from openpyxl
import Workbook
#creates a new workbook
wb = Workbook()
#Gets the first active worksheet
ws = wb.active
#creating new worksheets by using the create_sheet method

ws1 = wb.create_sheet("sheet1", 0) #inserts at first position
ws2 = wb.create_sheet("sheet2") #inserts at last position
ws3 = wb.create_sheet("sheet3", -1) #inserts at penultimate position

#Renaming the sheet
ws.title = "Example"

#save the workbook
wb.save(filename = "example.xlsx")

READING DATA FROM WORKBOOK

We load the file using the function load_Workbook() which takes the filename as an argument. The file must be saved in the same working directory.

#loading a workbook
wb = openpyxl.load_workbook("example.xlsx")

GETTING SHEETS FROM THE LOADED WORKBOOK

#getting sheet names
wb.sheetnames
result = ['sheet1', 'Sheet', 'sheet3', 'sheet2']

#getting a particular sheet
sheet1 = wb["sheet2"]

#getting sheet title
sheet1.title
result = 'sheet2'

#Getting the active sheet
sheetactive = wb.active
result = 'sheet1'

ACCESSING CELLS AND CELL VALUES

#get a cell from the sheet
sheet1["A1"] <
  Cell 'Sheet1'.A1 >

  #get the cell value
ws["A1"].value 'Segment'

#accessing cell using row and column and assigning a value
d = ws.cell(row = 4, column = 2, value = 10)
d.value
10

ITERATING THROUGH ROWS AND COLUMNS

#looping through each row and column
for x in range(1, 5):
  for y in range(1, 5):
  print(x, y, ws.cell(row = x, column = y)
    .value)

#getting the highest row number
ws.max_row
701

#getting the highest column number
ws.max_column
19

There are two functions for iterating through rows and columns.

Iter_rows() => returns the rows
Iter_cols() => returns the columns {
  min_row = 4, max_row = 5, min_col = 2, max_col = 5
} => This can be used to set the boundaries
for any iteration.

Example:

#iterating rows
for row in ws.iter_rows(min_row = 2, max_col = 3, max_row = 3):
  for cell in row:
  print(cell) <
  Cell 'Sheet1'.A2 >
  <
  Cell 'Sheet1'.B2 >
  <
  Cell 'Sheet1'.C2 >
  <
  Cell 'Sheet1'.A3 >
  <
  Cell 'Sheet1'.B3 >
  <
  Cell 'Sheet1'.C3 >

  #iterating columns
for col in ws.iter_cols(min_row = 2, max_col = 3, max_row = 3):
  for cell in col:
  print(cell) <
  Cell 'Sheet1'.A2 >
  <
  Cell 'Sheet1'.A3 >
  <
  Cell 'Sheet1'.B2 >
  <
  Cell 'Sheet1'.B3 >
  <
  Cell 'Sheet1'.C2 >
  <
  Cell 'Sheet1'.C3 >

To get all the rows of the worksheet we use the method worksheet.rows and to get all the columns of the worksheet we use the method worksheet.columns. Similarly, to iterate only through the values we use the method worksheet.values.

Example:

for row in ws.values:
  for value in row:
  print(value)

WRITING DATA TO AN EXCEL FILE

Writing to a workbook can be done in many ways such as adding a formula, adding charts, images, updating cell values, inserting rows and columns, etc… We will discuss each of these with an example.

CREATING AND SAVING A NEW WORKBOOK

#creates a new workbook
wb = openpyxl.Workbook()

#saving the workbook
wb.save("new.xlsx")

ADDING AND REMOVING SHEETS

#creating a new sheet
ws1 = wb.create_sheet(title = "sheet 2")

#creating a new sheet at index 0
ws2 = wb.create_sheet(index = 0, title = "sheet 0")

#checking the sheet names
wb.sheetnames['sheet 0', 'Sheet', 'sheet 2']

#deleting a sheet
del wb['sheet 0']

#checking sheetnames
wb.sheetnames['Sheet', 'sheet 2']

ADDING CELL VALUES

#checking the sheet value
ws['B2'].value
null

#adding value to cell
ws['B2'] = 367

#checking value
ws['B2'].value
367

ADDING FORMULAS

We often require formulas to be included in our Excel datasheet. We can easily add formulas using the Openpyxl module just like you add values to a cell.

For example:

import openpyxl
from openpyxl
import Workbook

wb = openpyxl.load_workbook("new1.xlsx")
ws = wb['Sheet']

ws['A9'] = '=SUM(A2:A8)'

wb.save("new2.xlsx")

The above program will add the formula (=SUM(A2:A8)) in cell A9. The result will be as below.

MERGE/UNMERGE CELLS

Two or more cells can be merged to a rectangular area using the method merge_cells(), and similarly, they can be unmerged using the method unmerge_cells().

For example:
Merge cells

#merge cells B2 to C9
ws.merge_cells('B2:C9')
ws['B2'] = "Merged cells"

Adding the above code to the previous example will merge cells as below.

UNMERGE CELLS

#unmerge cells B2 to C9
ws.unmerge_cells('B2:C9')

The above code will unmerge cells from B2 to C9.

INSERTING AN IMAGE

To insert an image we import the image function from the module openpyxl.drawing.image. We then load our image and add it to the cell as shown in the below example.

Example:

import openpyxl
from openpyxl
import Workbook
from openpyxl.drawing.image
import Image

wb = openpyxl.load_workbook("new1.xlsx")
ws = wb['Sheet']
#loading the image(should be in same folder)
img = Image('logo.png')
ws['A1'] = "Adding image"
#adjusting size
img.height = 130
img.width = 200
#adding img to cell A3

ws.add_image(img, 'A3')

wb.save("new2.xlsx")

Result:

CREATING CHARTS

Charts are essential to show a visualization of data. We can create charts from Excel data using the Openpyxl module chart. Different forms of charts such as line charts, bar charts, 3D line charts, etc., can be created. We need to create a reference that contains the data to be used for the chart, which is nothing but a selection of cells (rows and columns). I am using sample data to create a 3D bar chart in the below example:

Example

import openpyxl
from openpyxl
import Workbook
from openpyxl.chart
import BarChart3D, Reference, series

wb = openpyxl.load_workbook("example.xlsx")
ws = wb.active

values = Reference(ws, min_col = 3, min_row = 2, max_col = 3, max_row = 40)
chart = BarChart3D()
chart.add_data(values)
ws.add_chart(chart, "E3")
wb.save("MyChart.xlsx")

Result

How to Automate Excel with Python with Video Tutorial

Welcome to another video! In this video, We will cover how we can use python to automate Excel. I'll be going over everything from creating workbooks to accessing individual cells and stylizing cells. There is a ton of things that you can do with Excel but I'll just be covering the core/base things in OpenPyXl.

📄 Resources 📄
OpenPyXL Docs: https://openpyxl.readthedocs.io/en/stable/
Code Written in This Tutorial: https://github.com/techwithtim/ExcelPythonTutorial
Subscribe: https://www.youtube.com/c/TechWithTim/featured

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This Refcard dives into how a data lake helps tackle these challenges at both ends — from its enhanced architecture that’s designed for efficient data ingestion, storage, and management to its advanced analytics functionality and performance flexibility. You’ll also explore key benefits and common use cases.

Introduction

As technology continues to evolve with new data sources, such as IoT sensors and social media churning out large volumes of data, there has never been a better time to discuss the possibilities and challenges of managing such data for varying analytical insights. In this Refcard, we dig deep into how data lakes solve the problem of storing and processing enormous amounts of data. While doing so, we also explore the benefits of data lakes, their use cases, and how they differ from data warehouses (DWHs).

This is a preview of the Getting Started With Data Lakes Refcard. To read the entire Refcard, please download the PDF from the link above.

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