Is it possible to remove this loop? [SEC=UNCLASSIFIED]

Thank you all for providing various alternatives. They are all pretty fast. Great help! Based on a test of a dataset with 800,000 rows, the time used varies from 0.04 to 11.56 s. The champion is:

a1$h2 <- 0
a1$h2[a1$h1=="H"] <- 1

Regards,
Jin

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