Technical Notes

R Markdown is very nice way to write literate R code. Recently, reticulate became available, which bridges R and Python in R Markdown documents.

If you use Pipenv for Python dependency management, here's how you get reticulate to use the proper Python executable:

library('reticulate')
venv <- system("pipenv --venv", inter = TRUE)
use_virtualenv(venv, required = TRUE)
py_config()

The py_config() command should print out the path to the Python executable in the virtualenv created by Pipenv.

A very handy tip from Victor Afanasev:

Did you know that you can use Bundler inside single Ruby script (without Gemfile) and automatically install required dependencies for it?

# example.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'rest-client'
  gem 'nokogiri'
end

###

body = RestClient.get("https://www.reddit.com/r/ruby/").body

puts "Posts from r/ruby front page:"
Nokogiri::HTML(body).xpath("//div[contains(@class, 'scrollerItem')]//h2").each do |h2|
  puts h2.text.strip
end

By default, the Mac will display a giant padlock image when "Curtain Mode" is engaged with the Screens VNC app or macOS's built-in screen sharing capability:

I wanted to remove the padlock to avoid burn-in during long screen sharing sessions. I found this Apple Discussions post with the following instructions for overriding the default image:

• Create a picture using a graphics program, such as AppleWorks.
• Save the picture in PICT, TIFF, GIF, JPEG, or any other QuickTime-compatible static image format.
• QuickTime-compatible movies or QuickTime VR objects cannot be used.
  
• Name the picture "Lock Screen Picture".
  
• Copy the "Lock Screen Picture" file to /Library/Preferences/ on the client computer.

I was very dubious that it would work, but incredibly it does! If you save a plain black .tiff like this one as /Library/Preferences/Lock Screen Picture.tiff, the padlock image will disappear.

There is a relatively easy fix for a message from git lfs like:

Encountered n file(s) that should have been pointers, but weren't

If the files in question are already on a remote and you don't want to rewrite history, run:

git lfs migrate import --no-rewrite path/to/file.ext

This will create a new commit moving path/to/file.ext to LFS.

If you do need to rewrite history, see the documentation for migrating data to LFS.

To check whether this worked, run:

git lfs ls-files | grep path/to/file.ext

You should see an entry for path/to/file.ext in the resulting output.

I've found that Pocket's bookmarklet is not reliable in Safari and Safari Technology Preview due to browser security measures against 3rd party cookies. This results in their official bookmarklet asking me to "Please login" every time I try to use it.

Fortunately, there is an easy work-around with a very simple bookmarklet:

window.location.href = 'https://getpocket.com/edit?url='+encodeURI(window.location.href)

You can use the Bookmarklet Maker to turn this code into an actual bookmarklet.

This happened to me because I restored my boot disk from a full disk clone (thanks to a bad macOS update installation). I didn't want to restore to an unencrypted disk, so when I booted from my backup disk to do the restore, I used Disk Utility to encrypt my internal boot disk with a password.

After encrypting and then cloning the backup to my boot drive, I was greeted with a screen like this on my first boot from my boot drive:

Fine, no problem. I entered my disk password, and the normal login screen showed up. I entered my user password and everything was working...except I could not re-enable unlocking my disk with my user's password:

After searching around for how to fix failure of "Enable users" when "Some users are unable to unlock the disk", I discovered that there are a set of command line utilities for dealing with FileVault and I was able to fix the problem by decrypting the disk and then re-enabling FileVault.

Here's the command to decrypt: diskutil apfs decryptVolume /dev/disk1s1

To get "/dev/disk1s1", I simply looked at the info for my hard drive ("HD") in Disk Utility. (Normally this would be named "Macintosh HD", but I always rename mine.)

Then I simply re-enabled FileVault through System Preferences.

Warning: Messing around with disk encryption (or messing around with anything involving your boot disk) is risky. Always have a known good backup before you try anything like this, and proceed at your own risk – I am not responsible if you break your disk trying to follow these instructions.

I've found a few decent ways to extract all the tweets from a "tweetstorm" for easier reading or quoting:

• Thread reader
• Spooler
• tweetstorm.io has a nice landing page but isn't working as of writing.

When using PyCharm for debugging data science code, I often want to view a Pandas DataFrame from PyCharm's interactive debugger. It took me a bit to figure out how to do this from the keyboard — here's what I do:

1. While debugging, open the "Evaluate" window (bound to cmd-; in my configuration).
2. Type in the name of the variable for the DataFrame and press enter, which gives me this:

   
3. Now the question is how to activate the "View as DataFrame" button with the keyboard (see green arrow above). Turns out you can bind "View as Array" to a keyboard shortcut, which will also trigger "View as DataFrame". So I tab from the "Expression" text field to the "Results" area and then hit my "View as Array" shortcut (cmd-enter). This opens the DataFrame in SciView.

Here's the "View as Array" keyboard shortcut configuration:

I've found "floating mode" to work best with SciView. cmd-w will close SciView in floating mode, but for some reason when I do this, the "Evaluate" window will lose focus and I can't figure out how to focus it again without mousing. Keyboard Meastro to the rescue here:

Source: var x = /twitter.com\/.*\/status\/([0-9]+)/.exec(window.location.href); if(x == null) {alert("Doesn't look like this is a tweet.")} else {window.location='twitterrific:///tweet?id='+x[1]};

Converted to bookmarklet: javascript:(function()%7Bvar%20x%20%3D%20%2Ftwitter.com%5C%2F.*%5C%2Fstatus%5C%2F(%5B0-9%5D%2B)%2F.exec(window.location.href)%3B%20if(x%20%3D%3D%20null)%20%7Balert(%22Doesn't%20look%20like%20this%20is%20a%20tweet.%22)%7D%20else%20%7Bwindow.location%3D'twitterrific%3A%2F%2F%2Ftweet%3Fid%3D'%2Bx%5B1%5D%7D%7D)()

This is directly from macscripter.net, but they have some encoding issues that I've fixed: