Category: Technology Specific Entries

Installing the data.table package on Amazon Linux – LEMRS v0.6

This week I’ve upgraded the server to LEMRS v0.6, which adds three R packages for meta-analysis, esc, metafor, and robumeta.

The esc package requires another, much larger R package called data.table. That package, however, wouldn’t install. Like many R packages, data.table required the installation to do an automatic compilation of code written in C, but the C compiler couldn’t find some of the files it needed. This is because Amazon Linux uses non-standard folder locations for many of those files.

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LEMRS v0.5 – Adding rvest and aws.signature

I’ve been having problems with the web version of the Open-Meta app crashing with a C stack usage error. I entered an issue on the Shiny Server Github page and with the help of others who have had this problem, now suspect that the error is caused by the rJava package, which is required by mailR, the package I’ve been using to send email.

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Shiny button observer update: ignoring clicks on disabled buttons

In earlier posts, I’ve explained how to add a bit of JavaScript/jQuery code to your project that lets you have one Shiny observeEvent() handler for all your button and anchor clicks. This week I needed disabled buttons, which are easy to do visually by adding the Bootstrap disabled class to the button. But the buttons still responded to being clicked.

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How to source a mysqldump file with syntax statements

MySQL provides an external program called mysqldump that writes a file full of MySQL syntax statements that will recreate a database’s tables and their contents. Back in the Apple II days this kind of file was called an exec file. Windows calls them batch files and Linux calls them shell scripts, of which one common format is the bash file. You can create the same thing with HeidiSQL by right-clicking on the database you want to save or duplicate and selecting Export database as SQL.

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Why is my logical && comparison producing NA?

Who knew? I thought the difference between & and && for ANDing logical vectors in R was just that & evaluated the whole expression while && started at the left and went right until it hit a FALSE value. But there’s more. & is vectorized, but && only considers the first value in a vector and only returns a single value.

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Let’s put the whole Tidyverse on Amazon Lightsail (LEMRS v0.3)

The Tidyverse is a collection of related R packages, many of which I use on Open-Meta. I recently added the entire Tidyverse to my Windows-based development system, which meant I had to do the same to move that code to my Amazon Lightsail instance, which I did yesterday.

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How Shiny’s invalidateLater() actually works

Shiny’s invalidateLater() function, if you know about it at all, probably doesn’t work the way you think it does. Moreover, the way it actually does work, it turns out, is way cooler than the way it appears to work!

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Adding anchors to our Shiny button observer

In my previous post, I demonstrated a JavaScript / jQuery event handler that waits for button clicks and sends the id of the button that was clicked to a single observeEvent() in Shiny. In this post I’m going to improve that code while also extending it to include anchor tags (<a id="xxx">). Anchor tags are typically used to create links and include an href attribute that holds the URL of the linked document.

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One observer for all buttons in Shiny using JavaScript / jQuery

One of the profound limitations of Shiny is the way it supports buttons. Buttons are based on a function called actionButton(). When a button is clicked, Shiny reports the click on input$button_id. Every button has to have a unique id, which means that each button also has to have its own observer to watch for a click. But what if you want to do something like this:

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