Sequence Cleaner

Latest revision as of 23:30, 9 July 2011

Description

I want to share my script using biopython to clean sequences up , you should know analyzing poor data takes CPU time and interpreting the results from poor data takes people time, so it's always important to make a preprocessing.

Let me call my script as “Sequence_cleaner” and the big idea is to remove duplicate sequences, remove too short sequences ( the user defines the minimum length) and remove sequences which have too many unknown nucleotides (N) ( the user defines the % of N is allows ) and in the end the user can choose if he/she wants to have a file as output or print the result.

Script

from Bio import SeqIO
 
def sequence_cleaner(fasta_file,min_length=0,por_n=100):
    #create our hash table to add the sequences
    sequences={}
 
    #Using the biopython fasta parse we can read our fasta input
    for seq_record in SeqIO.parse(fasta_file, "fasta"):
        #Take the current sequence
        sequence=str(seq_record.seq).upper()
        #Check if the current sequence is according to the user parameters
        if (len(sequence)>=min_length and (float(sequence.count("N"))/float(len(sequence)))*100<=por_n):
       # If the sequence passed in the test "is It clean?" and It isnt in the hash table , the sequence and Its id are going to be in the hash
            if sequence not in sequences:
                sequences[sequence]=seq_record.id
       #If It is already in the hash table, We're just gonna concatenate the ID of the current sequence to another one that is already in the hash table
            else:
                sequences[sequence]+="_"+seq_record.id
 
 
    #Write the clean sequences
 
    #Create a file in the same directory where you ran this script
    output_file=open("clear_"+fasta_file,"w+")
    #Just Read the Hash Table and write on the file as a fasta format
    for sequence in sequences:
            output_file.write(">"+sequences[sequence]+"\n"+sequence+"\n")
    output_file.close()
 
 
 
#sequence_cleaner("Aip_coral.fasta",10,10)

You should call the function 'sequence_cleaner', there are 3 basic parameters:

        #1st: your fasta file 
        #2nd: the user defines the minimum length (default value 0 ( It means you don't have to care about the minimum lenght)
        #3rd: the user defines the % of N is allowed (default value 100 ( It means  you dont care to 'N' in your sequences))

FYI if you don't care about the 2nd and the 3rd parameters you are just gonna remove the duplicate sequences

Questions, Suggestions or Improvement

Send an email to genivaldo.gueiros@gmail.com