Ruby: Sorting an array with multiple fields

I was working on a project today and needed to make some changes to the way an array on objects was sorted before being displayed on the screen. The main reason I even bothered to post this is to heap a little more praise on Ruby for working the way I expected it to work.

Here was my object (not tied to a database, just created for convenience):

class Force
attr_accessor :id
attr_accessor :last_name
attr_accessor :first_name
attr_accessor :rank
attr_accessor :shift
attr_accessor :promoted_on
attr_accessor :phone
attr_accessor :totalcount
end

I needed to sort an array of these objects by rank ascending, shift ascending, then promoted_on (date) descending.

I sorted them by concatenating the fields together and making the right comparisons. This only works because the first two fields, rank and shift, cannot be empty. Otherwise, a simple concatenation would create undesired results.

Sorting all fields ascending looks like this:

@forces = @forces.sort {|x,y| x.shift + x.rank + x.promoted_on.to_s <=> y.shift + y.rank + y.promoted_on.to_s}

To sort the promoted_on field in descending order, reverse the x,y sides for that field:

@forces = @forces.sort {|x,y| x.shift + x.rank + y.promoted_on.to_s <=> y.shift + y.rank + x.promoted_on.to_s}

No need for a special sort coding block. Ruby FTW!

Steve Jobs RIP

Steve Jobs RIP

The Chromium OS experiment

Google's Chromium OS

I downloaded a bootable ISO of the Google Chromium OS release candidate. Then, fired it up in VMware Player and took a look around. It appears to be based on OpenSUSE Linux 11.4. SUSE was one of the distributions I cut my teeth on in the Linux world. I always appreciated the 9 pound manual of documentation that came with it. Very helpful for beginners and a good reference to their tools.

I might have made a mistake when setting up the virtual machine because it complained of low memory right after booting. This could also explain the slow performance I experienced. The desktop itself is clean and appears to be optimized to run the Chrome web browser. There was a local word processing application, but I didn't get far enough to test it out, it was just too slow. I could not find a download link at Google, but I found one at a .eu domain. Maybe it was a pirated or tampered version. I am going to postpone further research until I am sure I have a good distribution.

Updated: Turns out Google doesn't provide an image or download of the OS itself, only the source code and compilation instructions. Also, the OS is based on Ubuntu, despite the build I got from Europe based on SUSE. ZD Net suggested that the running OS would be slow so I maybe I am not missing much at this stage of development. I don't want to pay for a Chromebook just to run Chrome. Another reason to keep this on hold for now.

Getting by in Git

Git is the source code management system used for the Linux kernel and many other highly complex projects. It was written by Linux Torvalds after some controversy over the proprietary Bitkeeper program that used to manage the Linux kernel.

I've needed to upgrade my skills recently to use git in place of subversion because that is what my shop decided to use. I've moved all my Rails code into a remote git server and so far, so good.

One improvement is it has fewer "droppings" than subversion. There is no hidden .svn directory in each directory with source code. Only a single .git directory at the root of the project, plus a .gitignore file for files you don't want git to track.

Initialize project tracking
git init

Check out an existing project from remote server
git clone ssh://server/git/project

Add a file for git to track
git add

Add all files from this directory and below for git to track
git add .

Commit all files to local repository
git commit -a -m "message"

Undo changes to a file (re-check out from repository)
git checkout --

Pull files from remote repository and merge with local repository
git pull

Push files to remote repository (must commit first)
git push

Move file or directory to new location
git mv path destination

Remove file or directory from the working tree
git rm path

To create a remote repository from an existing project takes several steps
cd /tmp
git clone --bare /path/to/project (creates a /tmp/project.git directory)
scp project.git to remote server
cd /path/to/project
git remote add origin ssh://server/git/project
git config branch.master.remote origin
git config branch.master.merge refs/heads/master

LVM basics

I've just spent a few hours with iSCSI SAN disks (EqualLogic) and Linux Logical Volume Manager (LVM). The abstraction is even deeper than that, because Linux at work is running under VMware, so it is really VMware talking to the SAN and presenting a SCSI disk to Linux. Since I only get into the LVM weeds a couple of times a year, I thought it would be helpful to list the steps I took to get usable disk space under Linux starting with the raw disk space.

Step One - create a new partition
Create a new partition with FDISK or PARTED. Mark the partition type hex 8E for LVM. In my case, the SCSI disk appeared as /dev/sdb and the partition using all space became /dev/sdb1. LVM is capable of using a raw device (no partition type), but I stayed in familiar partitioning territory.

Step Two - create LVM physical volume
pvcreate /dev/sdb1

Step Three - create LVM volume group in the physical volume
vgcreate new_volume_group /dev/sdb1

Step Four - create LVM logical volume in the volume group
lvcreate --name new_logical_volume --size 100G new_volume_group

Step Five - create a file system on the logical volume
mkfs -t ext4 /dev/mapper/new_volume_group-new_logical_volume
Note: Linux device mapper automatically creates a symlink to the disk in /dev/mapper using the volume group and logical volume names. If you choose more meaningful names than the example, the name won't look so awful.

Step Six - turn off automatic file system checks (optional)
tune2fs -c 0 /dev/mapper/new_volume_group-new_logical_volume

Step Seven - add mount point in /etc/fstab
Once the mount point is list in fstab, mount it manually and it is ready to use.

Chrome Revisited

In my first serious test of Mac Chrome back in August, 2010, it came up short compared to other popular web browsers. But Chrome has been evolving fast. And since Firefox 4.0 was just released, it seemed like the right time to run another informal comparison.

What a difference. Chrome has become more stable, faster, and has made huge strides in available and useful plugins. The plugin gap with Firefox was a glaring issue last time. As a web developer, Firefox was indispensable with the Firebug plugin, letting you drill into the CSS and JavaScript acting on individual DOM components. Chrome now has native developer tools that rival Firebug. I am also fond of the Awesome Screenshot plugin that allows you to capture and annotate a web page from within the browser.

While I have found Firefox 4.0 a nice improvement in looks and rendering speed, I have also found it leaks memory, more so on Windows than Linux or Mac. I can rarely make it through a day without the Windows version locking up. That may be an artifact of the slew of plugins I am running and not the Firefox core.

For the last couple of weeks, I have been using Chrome as my primary browser on all platforms and have been very pleased. Competition is a great thing and I am excited to see browsers evolving again after what seemed like a long period of stagnation.

Android G2 and iTunes music sync

Getting music from iTunes on a Mac onto an Android G2 smart phone was an easy task. Maybe it wasn't so easy with the first generation Android phones, but the G2 I purchased a couple of weeks ago came with everything I needed.

Connecting the phone to the Mac

My main Mac is a two year old MacBook. The G2 came with a USB sync cable and as soon as I attached it, it opened iPhoto to upload pictures just like a camera. But the G2 also displayed a screen to enable it as a USB disk drive. I enabled disk mode, then took a look at the mounted volume in Finder.

One of the icons on the Volume was DoubleTwist. When I double clicked it, it started downloading the latest Mac version of DoubleTwist. After installation, the DoubleTwist interface looked very much like iTunes. It allows you to automatically sync all music from iTunes or just selections.

Since I don't plan to listen to music often on the G2, I chose to only sync playlists. This only syncs the music required in each playlist. There are a lot of options in DoubleTwist and the integration was seamless.

Automating FTP

People frequently need to automate FTP sessions to upload or download files.
Most command line FTP clients, including the FTP client on the Mac, can automatically login to an FTP server by reading the .netrc file in the user home directory. Note that the FTP auto-login file starts with a dot in front of the name (dot netrc).

Syntax of the $HOME/.netrc

The .netrc file can contain more than one auto-login configuration. Each FTP server has a set of commands, the minimum being the login name and password. You can create as many machine sections as you need. Here is a generic example:

machine ftp.server.com
  login myuserID
  password mypassword

Very Important: .netrc permissions!
Since user IDs and passwords are stored in the .netrc file, the FTP client enforces permission checking on it. It must be set so that no groups and no other users can read or write to it. You can set the permissions on it with this command from the Terminal (from your home directory) once the file is created:
chmod 700 .netrc

Adding FTP commands in a BASH script
You can embed FTP commands in a BASH script to upload and download files.
For example, you could create a script file named ftpupload.sh:

#!/bin/bash
# upload a file
/usr/bin/ftp -i ftp.server.com <<ENDOFCOMMANDS
cd backupdir
cd subdir
put datafile
quit
ENDOFCOMMANDS

In this example, I added the -i switch when running FTP to prevent it from prompting on multiple file uploads/downloads, even though it is only uploading one file in the example. I also use the BASH HERE document feature to send commands to FTP. When the script is run, it will auto-login using the information in the .netrc file, change to the right remote directory and upload the datafile.

Scheduling the script with Cron
The last step is to get the BASH script to run unattended, say every day at 5:00 am. The old school UNIX way is to use Cron, but the fancy new Apple way is to use a launchd XML configuration. As long as cron is supported in OS X, I'll stick to the old school way. I leave the launchd configuration as an exercise for the reader.

Add these lines with the command "crontab -e", then save:

# automated FTP upload
0 5 * * * /Users/username/ftpupload.sh