why its not possible to write-snplist (with Alleles and positions)

[Kevin Harper]

its would be far easier to merge by  snplists with matching alleles and positions
because there's many ids with different positions/alleles , 
how to get those exact matching snps from a data1 to merge with data2?

or alteast merge by matching allele and position and ignore duplicate ids with diffferent positions (not errors out) ..you understand this?

Thanks