\name{findCommonVariants}
\alias{findCommonVariants}
\title{Finding the common variants among all input VCF files}
\description{
The common variants (inc. SNPs and indels) among all the input files are found. A data frame containing these common variants is returned. The data frame has a similar format as VCF files. }
\usage{
  findCommonVariants(VCF_files)
}
\arguments{
  \item{VCF_files}{ a character vector giving the names of VCF format files.}
}
\details{
This function loads all variants (SNPs and indels) from the input VCF files, and find the common variants that are reported in all the VCF files. If a variant record in a input VCF file has multiple alternative sequences (split by `,'), each alternative sequence is treated as a single variant. Two variants in two VCF files are the same only if their genomic locations, their reference sequences, their alternative sequences and their variant types are identical.

This function currently does not support other types of variants other than SNPs and indels. 

There are eight columns in the returned data frame: chromosome name, position, identity, reference sequence, alternative sequence, quality, filter and extra information. The input may have more columns; these columns are not included in the data frame. If the identity, the quality, the filter and the extra information for the same variant are different among the input VCF files, those information associated with the lowest quality value of this variant among the VCF files is reported in the resulted data frame. For example, if an SNP on chrX:12345 (A=>G) is reported in all the three input VCF files, and the quality scores in the three VCF files are 100, 10, 50 respectively, the identity, the quality, the filter and the extra information in the second VCF file are reported in the resulted data frame for this SNP.
}
\value{ 
A data frame containing the common variants among all the input VCF files is returned. The first eight columns are: chromosome name, position, identity, reference sequence, alternative sequence, quality, filter and extra information.

If there are not any common variants, this function returns an NA value.
}
%\references{
%}
\author{Yang Liao and Wei Shi}

%\note{}
%\seealso{}
\examples{\dontrun{
# finding the common variants between to input VCF files: a.vcf and b.vcf
library(Rsubread)
findCommonVariants(c('a.vcf','b.vcf'))
}}
% Add one or more standard keywords, see file 'KEYWORDS' in the
% R documentation directory.
%\keyword{}
%\keyword{}% __ONLY ONE__ keyword per line
