options(stringAsFactor=F)
args <- commandArgs(T)
input_expr <- args[1]
output_expr <- args[2]

dat <- read.table(input_expr, header=F, row.names=1)

###compute mean expression level for each tissue/cell line
tissues <- unique(dat[,1])
mean_expr <- function(x){
    return(mean(dat[dat[,1]==x,2]))
}
out <- data.frame(sample=tissues)
out$mean_expr <- unlist(lapply(tissues, mean_expr))
write.table(out, output_expr, row.names=F, col.names=F, sep="\t", quote=F)