Hashes or Associative Arrays

1
Hashes or Associative Arrays

• Hashes begin with
• Hashes are similar to an array. The difference
  is that an array uses integers as index values
  but hashes uses arbitrary scalars called keys.
• Keys are used to retrieve values from a hash

2
For example

• An array A hash
• Element Value Key Value
• 0 Rob first name Rob
• 1 professor profession professor
• 2 UW-Parkside location UW-Park
• For the array, you have to access the contents
  using their index , for the hash you access
  values via keys

3
Hash syntax

• hash1 (key, element, key, element)
• Or
• hash1 (
• key gt element
• key gt element
• )
• Or can assign keys and values line by line in
  FASTA formatted files ftp//ftp.tigr.org/pub/data/
  

4
Operators for Hashes

• Keys() returns a list of all the current keys
• Values() returns a list of all current values
• Each() returns key-value pair as two element list
• Delete() removes both key and value from hash

5
A hash in action

• hash1 (
• first name gt Rob,
• profession gt professor,
• location gt UW-Parkside
• )
• Print Contents of hash \n
• Foreach k (keys hash1)
• Print k gt hash1k\n
• exit

Output Contents of hash First name gt
Rob Profession gt professor Location gt
UW-Parkside
6
Another look

• hash1 (
• first name gt Rob,
• profession gt professor,
• location gt UW-Parkside
• )
• Print Contents of hash \n
• Foreach v (values hash1)
• Print \v now contains v\n
• exit

Output Contents of hash v now contains Rob v
now contains UW-Parkside v now contains
professor
7
There are many actions you can perform on a hash

• Sort the hash by its keys or values
• Sort (keys hash1)
• Assign keys or values of a hash to an array
• _at_ary1 keys (hash1)
• Assign an individual hash entry to a variable
• var1 hash1k
• Delete an entry from a hash
• Delete hash1k

8
Homework

• Write a Perl program to transcribe and translate
  a FASTA-formatted DNA sequence (write the RNA to
  one file, write the translation (in all six
  frames) to another file). Use this program on
  AF315723 available in NCBI.

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More homework

• Write a Perl program to identify protein
  sequences in D.radiodurans with more than 4
  cysteines. Go to TIGR FTP, look for file GDR.pep
• Hint