Factorize each of the following expression:

$x^{2}+y-x y-x=\left(x^{2}-x y\right)+(y-x) \quad[$ Regrouping the expressions $]$

$=x(x-y)+(y-x)$        

$=x(x-y)-(x-y)$      $[\because(y-x)=-(x-y)]$

$=(x-1)(x-y)$        $[$ Taking $(x-y)$ as the common expression $]$