Let $x = x ( y )$ be the solution of the differential equation $y ^ { 2 } \mathrm {~d} x + \left( x - \frac { 1 } { y } \right) \mathrm { d } y = 0$. If $x ( 1 ) = 1$, then $x \left( \frac { 1 } { 2 } \right)$ is :\\
(1) $\frac { 1 } { 2 } + \mathrm { e }$\\
(2) $3 + e$\\
(3) $3 - e$\\
(4) $\frac { 3 } { 2 } + e$