title: Center text layer in ggplot barchart
body: <p>I have a histogram with some text and I m trying to center it for the corresponding type</p>
  
  <pre><code>df = read.table(text = "
  id   year  type amount
                  1  1991  HIIT     22
                  2  1991 inter    144
                  3  1991  VIIT     98
                  4  1992  HIIT     20
                  5  1992 inter    136
                  6  1992  VIIT    108
                  7  1993  HIIT     20
                  8  1993 inter    120
                  9  1993  VIIT    124
                  10 1994  HIIT     26
                  11 1994 inter    118
                  12 1994  VIIT    120
                  13 1995  HIIT     23
                  14 1995 inter    101
                  15 1995  VIIT    140
                  16 1996  HIIT     27
                  17 1996 inter    103
                  18 1996  VIIT    162
                  19 1997  HIIT     24
                  20 1997 inter     96
                  21 1997  VIIT    172
                  22 1998  HIIT     24
                  23 1998 inter     92
                  24 1998  VIIT    177
                  25 1999  HIIT     28
                  26 1999 inter     45
                  27 1999  VIIT    220
                  28 2000  HIIT     26
                  29 2000 inter     36
                  30 2000  VIIT    231", header = TRUE, sep = "")
  library(dplyr);
  library(ggplot2);
  library(scales);
  
  df %&gt;%
    mutate(type = factor(type, levels = c("inter",  "VIIT", "HIIT"))) %&gt;%
    group_by(year) %&gt;%
    mutate(ratio = amount/sum(amount),
           pos=cumsum(ratio)-ratio/2) %&gt;%
    ggplot(aes(x=factor(year), y=ratio, fill=type)) +
    geom_bar(stat="identity") +
    geom_text(aes(y = pos, label = percent(pos)), size = 4) +
    scale_y_continuous(name="", labels = percent) +
    coord_flip()
  </code></pre>
  
  <p>My plot look like :
  <a href="https://i.stack.imgur.com/ohCPq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ohCPq.png" alt="enter image description here"></a></p>
  
  <p>Can you help me to solve this problem because I have no idea how to fix it with the position parameter </p>
  
  <p>Thanks</p>