Appending % sign in output of prop.table

Another solution could be replacing content of matrix:

m2 <- m
m2[] <- sprintf("%.1f%%",round(prop.table(m,1)*100, 3))
m2
#   C       D      
# A "25.0%" "75.0%"
# B "33.3%" "66.7%"

Most functions designed to work with vectors also accept matrices but return a vector instead of a matrix: paste, sprintf, etc. You can use apply, that will return a matrix.

apply( 
  prop.table(m,1)*100, 
  2, 
  function(u) sprintf( "%.1f%%", u ) 
)

There's a package called janitor that takes care of the prop.table() "format-as-percentage" problem. Here's a link to the package: https://github.com/sfirke/janitor

Here's a usage example from the github page.

roster %>%
  tabyl(employee_status, full_time) %>%
  adorn_totals("row") %>%
  adorn_percentages("row") %>%
  adorn_pct_formatting() %>%
  adorn_ns() %>%
  adorn_title("combined")
#>  employee_status/full_time         No        Yes
#>             Administration   0.0% (0) 100.0% (1)
#>                      Coach 100.0% (2)   0.0% (0)
#>                    Teacher  33.3% (3)  66.7% (6)
#>                      Total  41.7% (5)  58.3% (7)