```
pmatch("", "") # returns NA
pmatch("m", c("mean", "median", "mode")) # returns NA
pmatch("med", c("mean", "median", "mode")) # returns 2
pmatch(c("", "ab", "ab"), c("abc", "ab"), dup = FALSE)
pmatch(c("", "ab", "ab"), c("abc", "ab"), dup = TRUE)
## compare
charmatch(c("", "ab", "ab"), c("abc", "ab"))
```

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