travis build failing because devtools is missing Introduction to Travis CI and R Package Development Travis CI is a popular continuous integration platform used by many developers and organizations to automate the testing of their software projects. In this article, we will focus on setting up a Travis CI build for an R package using the devtools package. Background: Installing devtools Manually The first issue that arises when trying to install the devtools package in a Travis CI build is related to its dependencies.

Grouping by Date and ID with Average Price: A Step-by-Step Guide In this article, we will explore how to calculate the average price per rider and per day in a table, as well as the overall average. We’ll cover both SQL and MySQL examples, including using the WITH ROLLUP modifier. Understanding the Problem Let’s start by analyzing the problem at hand. We have a table with three columns: id, price, and date.

Calculating Speed from Needle Angle: A Technical Deep Dive Introduction Creating a manual speedometer control that accurately displays the corresponding speed from an angle is a fascinating project. In this article, we will delve into the mathematical concepts and technical details required to achieve this goal. We will explore how to convert the needle’s angle to speed using trigonometry, discuss the assumptions made in the calculation, and provide a step-by-step guide on implementing this solution.

String Concatenation in SQL: A Deep Dive into PostgreSQL and MySQL Introduction When working with databases, it’s common to need to concatenate strings with other data types. In this article, we’ll explore how to achieve string concatenation in two popular databases: PostgreSQL and MySQL. Understanding the Problem The problem presented in the original Stack Overflow question is a classic example of string concatenation in SQL. The goal is to add strings before fields contained in a specific column.

Understanding UIView Hides on Textfield Tap: A Deep Dive Introduction As developers, we often encounter peculiar behaviors in our iOS applications. In this article, we’ll delve into a common issue where a UIView named “NewAddressView” hides automatically when tapped on its underlying UITextField. We’ll explore the reasons behind this behavior and provide a solution to bring the view back to the front. Background In Objective-C, when you create a custom UIViewController, you can add subviews using the view.

Understanding and Implementing Video Playback in iPad Applications Introduction When building an iPad application that involves playing video files, one of the most common challenges developers face is accessing and playing these videos within their app. In this article, we’ll delve into the details of how to play a video file from the Documents folder on an iPad using the MPMoviePlayerViewController class. Background The process of accessing and playing media files in iOS applications involves several steps:

Understanding and Customizing Axis Labels in Facet Wrap When working with facet wrap in ggplot2, it’s common to encounter issues related to the appearance of horizontal axis labels. In this post, we’ll explore how to remove additional lines below horizontal axis labels when using geom_col and facet_wrap. Introduction to Facet Wrap Facet wrap is a powerful feature in ggplot2 that allows you to create multiple plots on the same axes. It’s commonly used for visualizing categorical data across different groups or sectors.

Faster Function Than Aggregate() in R: A Comparative Analysis The aggregate() function is a powerful tool in R for aggregating data by a specified column or group. However, it can be slow when dealing with large datasets. In this article, we will explore alternative approaches to performing aggregations in R, focusing on the use of the Tidyverse, base functions, and plyr packages. Background The aggregate() function is part of the built-in R package and uses the data.

Understanding SQL Insert Statements: A Deep Dive into Multi-Row Inserts and Error Handling Introduction to SQL and Table Structure Before we dive into the world of multi-row inserts, it’s essential to understand the basics of SQL and table structure. SQL (Structured Query Language) is a programming language designed for managing and manipulating data stored in relational database management systems (RDBMS). A table is a fundamental concept in RDBMS, representing a collection of related data.

Adding Totals and Adjusting Row Location in a Data Frame In this article, we will explore how to add totals for rows and columns in a data frame using the janitor package. We’ll also discuss how to adjust the location of rows when dealing with non-numeric values. Introduction The janitor package is a popular choice among R users for adding totals and adjusting row locations in data frames. It provides an easy-to-use interface for performing these tasks, making it a valuable tool in any data analysis workflow.