ECML16: GaKCo: a Fast Gapped k-mer string Kernel using Counting
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README.md

GaKCo-SVM

GaKCo is a fast and naturally parallelizable algorithm for gapped k-mer based string kernel calculation. GaKCo uses associative arrays to calculate the co-occurrence of substrings using cumulative counting. The algorithm easily scales to large dictionary sizes and high numbers of mismatches.

Reference Paper

Link: GaKCo: a Fast GApped k-mer string Kernel using COunting

Included Datasets

We perform 19 different classification tasks to evaluate the performance of GaKCo. The tasks pertain to three categories:

    (1) TF binding site prediction (DNA dataset)
    (2) Remote Protein Homology prediction (protein dataset)
    (3) Character-based English text classification (text dataset)

Installation

Download and extract this repository, then enter:

    $ cd src
    $ make all install

An executable file named GaKCo should now be located in your GaKCo-SVM/bin directory.

Tutorial

Running GaKCo

GaKCo takes several arguments:

    Usage: ./GaKCo -g <int> -k <int> -n <int> -p <int> <sequenceFile> <dictionaryFile> <labelsFile> <kernelFile>
    
    Arguments:
        g : length of gapped instance. Constraints: 0 < g < 20
        k : length of k-mer. Constraints: k < g
        n : (optional) maximum number of examples in the data set. Default: 15000 [This value can be increased or decreased according to the memory capacity of the machine]
        p : (optional) parallel. Set to 1 to using multithreading; else set to 0. Default: 1
        sequenceFile : set of sequences (see "Sequence File Format" section below for details on how this file should be formatted)
        dictionaryFile : file containing the alphabet of characters that appear in the sequences (simple text file)
        labelsFile : name of file to place labels from the examples (simple text file). This file is used by GaKCo to create create the kernel matrix
        kernelFile : name of the file to write the kernel that will be computed by GaKCo.

For example:

    $ ./GaKCo -g 7 -k 5 -n 15000 -p 1 mySequences.fasta data/protein.dictionary.txt labelsFile.txt computedKernel.txt

Or:

    $ ./bin/GaKCo -g 7 -k 5 -n 15000 -p 1 mySequences.fasta data/protein.dictionary.txt labelsFile.txt computedKernel.txt

Output

GaKCo computes the kernel function for all pairs of sequences in the provided sequence file, thus giving the "distance" or "similarity" values needed for an SVM classifier. The resultant kernel matrix will be written to the kernelFile argument.

Running GaKCo with the RUN.sh script

You can run GaKCo using the RUN.sh script after completing the "Installation" instructions above. This option is useful if you have separate training and testing files and want to create a training set kernel file and a testing set kernel file.

    $ bash RUN.sh <trainingFile.fasta> <testingFile.fasta> <dictionaryFile.txt>

Example:

    $ bash RUN.sh data/1.1.test.fasta data/1.1.train.fasta data/protein.dictionary.txt

Alternatively, you can simply use the following to call the RUN.sh script with default hard-coded values:

    $ bash RUN.sh

You can change the default values by opening RUN.sh and changing the file names (located on lines 8, 9, 10). You can change the default parameter values by modifying lines 32-35.

Output

The script places the computed test and kernel files in the GaKCo-SVM/results directory.

Sequence File Format

The sequenceFile argument to GaKCo must be a file in the following format:

>label
sequence
>label
sequence
...

Where label are class labels (-1 or 0 for negative class and 1 for positive class) and sequence lines are a sequence contained in a single line (sequences running over multiple lines will not be handled correctly). The first line of the file should be a label line. For example:

>1
MKTPITEAIAAADNQGRFLSNTELQAVNGRYQRAAASLEAARSL
>1
MLDAFAKVVAQADARGEFLSNTQLDALSKMVSEGNKRLD
>0
FPTIPLSRLADNAWLRADRLNQLAFDTYQEFEEAYIPKEQIHSFWWNPQ