[R] String position character replacement

[Yang, Joy (NIH/NHGRI) [F]]

Hi,

Is there a way to efficiently replace specified indices in a string with another character? For example, if I had a vector of strings such as

[1] "hellohowareyoudoing"
[2] "imgoodhowareyou"
[3] "goodandyou"
[4] "yesimgoodijusttoldyou"
[5] "ohyesthatsright"

and had a list of positions that I want to replace with the character "-"

[[1]]
[1]  3  9

[[2]]
[1]  3  4

[[3]]
[1]  4  7

[[4]]
[1] 5 6 7 8 9

[[5]]
[1]  2  5  7 12

I would like to get

[1] "he-lohow-reyoudoing"
[2] "im--odhowareyou"
[3] "goo-an-you"
[4] "yesi-----ijusttoldyou"
[5] "o-ye-t-atsr-ght"

Is there an easy way to do this? Or would the easiest way be writing a function to take substrings of the original vector and pasting in the replacement character?

Thanks in advance!
Joy