Distinct dumb-mongodb-name

You are forbidden to use some characters in a mongodb database name, e.g., ?, !, #, @, %, ^, *, .,   or starts with a $.  Any other UTF8 characters are valid.

There are other characters that you can use but can cause difficulties, e.g., the dash "-" character.

If you want to find the distinct values of a certain field, e.g., "location_type", in a database that has a dash in its name, you can get what you want using a mongo query like this:

> db.getSiblingDB("dumb-mongodbname").runCommand ({ distinct: 'location_type', key: 'destinationType' })
{
"values" : [
"REGION",
"CITY",
"COUNTRY"
],
"stats" : {
"n" : 999,
"nscanned" : 999,
"nscannedObjects" : 999,
"timems" : 3,
"cursor" : "BasicCursor"
},
"ok" : 1
}


If you try to reference the dumb-mongodb-name, with the dashes in the name, you'll get an error like this:


> db.dumb-mongodbname.location.find().skip(0).limit(30)
Mon Feb 11 10:13:51 ReferenceError: mongodbname is not defined (shell):1

References

http://docs.mongodb.org/manual/reference/command/distinct/
https://jira.mongodb.org/browse/SERVER-3229
http://stackoverflow.com/questions/7975185/mongodb-query-over-a-hash-with-special-chars-in-keys/7976235#7976235

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System Restore from Networked Time Capsule

The main trick to getting a system restore to work from a networked Time Capsule (TC) is to set the password for the sparsebundle (backup) file.

Open the Airport Utility

Select "Disk Password", as opposed to "Device Password" as the password type for your TC.

Chose a password that you will remember and update the TC.

Connect to the TC via the finder

Open the Finder  |  Go  |  Network

Choose your TC device from the list

Click "Connect as..." button

It will prompt with a dialog that says: Enter your password for the server <TC Name>.

Open Terminal Window

Go to /Volumes/TCDirectory

Change sparsebundle File Password

Run the following command to set the password for the sparsebundle file:

sudo hdiutil chpass /path/to/filename.sparsebundle

Restore from Time Machine Backup

Restart your Mac

Press command + R when you hear the chime.

This will bring up the Mac OSX Utilities dialog window

Choose Restore from Time Machine Backup

Choose your TC | Choose TC disk backup name 

It will ask for a password.

Enter the password you entered in the hdiutil command

Now, you will presented with a list of backups you can restore from.

It will take a long time (perhaps 4+ hours)  to perform the restore.

References

http://www.youtube.com/watch?v=aca8Zfiowtw
https://discussions.apple.com/thread/3182224?start=0&tstart=0
http://pondini.org/TM/14.html

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My Work Clock and Functional Programming

Programming in Scala has made me a better Ruby programmer.  Thank you Scala!

Functional Iterators

I appreciate Functional Iterators much better now.

Given a list of items:

• If you want to return a single value, after iterating through the list, use reduce.
• If you want to return a subset of the values, use filter.
• If you want to return a new list, where each item as likely been transformed, use map.

Example of Using Reduce

Below, is an example of iterating through my list of billable hours in a week to arrive at a single value -- then total number of hours I worked that week for that client.

I use a simple app, My Work Clock, on my phone to track my billable hours.

I simply "Punch In" when I start working and "Punch Out" when I'm done.

It produces a report that I can email to myself in CSV format, which I then open in Libre Office (like MS Excel).

I copy/paste the hours into a Ruby console and run in through a functional programming one-liner to determine my weekly billable hours:


~ $ irb
irb(main):001:0> s =<<TEXT
irb(main):002:0" 8.02
irb(main):003:0" 13.72
irb(main):004:0" 15.87
irb(main):005:0" 10.87
irb(main):006:0" 8.13
irb(main):007:0" TEXT
=> "8.02\n13.72\n15.87\n10.87\n8.13\n"

irb(main):008:0> s.split.reduce(0){|sum, value| sum.to_f + value.to_f}

=> 56.61

Example of Using a Filter

The select function takes two arguments:

• The list:  ["8.02", "13.72", "15.87", "10.87", "8.13"]
• Function to apply on each item value; Return only those greater than 10:  number.to_f > 10

# Daily work hours greater than 10 hours

["8.02", "13.72", "15.87", "10.87", "8.13"].select {|number| number.to_f > 10}

=> ["13.72", "15.87", "10.87"]

Example of Using a Map

The map function will return an Array composed of results from the block operation.

The map function takes two arguments:

• The list of days:  days = %w{ 2013-01-18 2013-01-17 2013-01-16 2013-01-15 2013-01-14 }
• Function to apply on each item value:  day_hours_hash[d]

Here's the hash:
day_hours_hash = {"2013-01-18" => "8.02", "2013-01-17" => "13.72", "2013-01-16" => "15.87", "2013-01-15" => "10.87","2013-01-14" =>"8.13"}


# Return the number of hours worked for each day

days.map {|d| day_hours_hash[d]}

=> ["8.02", "13.72", "15.87", "10.87", "8.13"]

References 

http://ruby-doc.org/core-1.9.3/Enumerable.html

http://railspikes.com/2008/8/11/understanding-map-and-reduce

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