Substituting Greek symbols in some tick labels

I have a character vector that I'm using to label ticks in a  
dotchart. Some
of the elements in the vector have an asterisk (*) where a Greek Delta
needs to be placed when the plot is generated. Here's a simple  
example:

x <- 1:4
x.lab <- c("a*a", "bbb", "c*c", "ddd")
dotchart(x, labels = x.lab)

The first and third labels should be 'a<Delta>a' and 'c<Delta>c'. I've
tried things like,

x.lab <- strsplit(x.lab, "[*]")
x.lab <- lapply(x.lab, function(y) expression(paste(y, sep = Delta)))
The plotmath function paste has no sep argument.

Do you want to do this "by hand"? (Since you have not offered values  
of 'y'.)

x.lab <- expression( a*Delta*a, bbb, c*Delta*c, ddd)

#   Note use of "*" and no quotes in an expression vector.

  x <- 1:4
dotchart(x, labels = x.lab)
David.

>
> but because 'y' is unevaluated, the resulting list elements won't  
> work as
> tick labels. I've tried to modify it by using bquote and substitute,  
> but
> couldn't get anything closer. Any suggestions? Thanks!
>
> Cheers,
> eric
>
> -- 
>
> Eric Archer, Ph.D.
> Southwest Fisheries Science Center
> NMFS, NOAA
> 8901 La Jolla Shores Drive
> La Jolla, CA 92037 USA
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>
> Marine Mammal Genetics Group: swfsc.noaa.gov/prd-mmgenetics
> ETP Cetacean Assessment Program: swfsc.noaa.gov/prd-etp
>
> "The universe doesn't care what you believe.
> The wonderful thing about science is that it
>   doesn't ask for your faith, it just asks
>   for your eyes."  - Randall Munroe
>
> "Lighthouses are more helpful than churches."
>   - Benjamin Franklin
>
>   "...but I'll take a GPS over either one."
>       - John C. "Craig" George
>
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David Winsemius, MD
Alameda, CA, USA

Substituting Greek symbols in some tick labels

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