Major hospital operators say they will comply with new rules to make public their prices for medical procedures starting Friday, exposing previously secret market rates in an industry that accounts for about 6% of the U.S. economy. The roughly $1.2 trillion hospital sector will begin posting prices publicly in the New Year after losing a legal challenge to overturn new transparency rules that are a centerpiece of the Trump administration’s health-care policy. Health and Human Services Secretary Alex Azar said earlier in December the hospital pricing data and other transparency rules put forward by the administration were fundamental to a...