title: How to draw stacked bars in ggplot2 that show percentages based on group?
body: <p>My data frame is  </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
  31 2001  HIIT     29
  32 2001 inter     30
  33 2001  VIIT    233
  34 2002  HIIT     37
  35 2002 inter     35
  36 2002  VIIT    221
  37 2003  HIIT     41
  38 2003 inter     34
  39 2003  VIIT    218
  40 2004  HIIT     28
  41 2004 inter     38
  42 2004  VIIT    226
  43 2005  HIIT     34
  44 2005 inter     41
  45 2005  VIIT    216
  46 2006  HIIT     28
  47 2006 inter     40
  48 2006  VIIT    222
  49 2007  HIIT     37
  50 2007 inter     42
  51 2007  VIIT    199
  52 2008  HIIT     35
  53 2008 inter     60
  54 2008  VIIT    185
  55 2009  HIIT     47
  56 2009 inter     51
  57 2009  VIIT    181
  58 2010  HIIT     44
  59 2010 inter     44
  60 2010  VIIT    174
  61 2011  HIIT     44
  62 2011 inter     47
  63 2011  VIIT    171
  64 2012  HIIT     37
  65 2012 inter     49
  66 2012  VIIT    178", header = TRUE, sep = "")
  &gt; 
  </code></pre>
  
  <p>I want to draw stacked barplots for each year. These barplot should show percentages of ("inter", "VIIT","HIIT") within each year. I have used the following codes, but that give percentages of the whole column (amount) total, not within year total. </p>
  
  <p>My codes are:</p>
  
  <pre><code>library(ggplot2)
  
  ggplot(df, aes(x=factor(year), fill = factor(type),
              y = amount/sum(amount)*100)) +
    xlab("Trade Type")+
    ylab(" % share") +
    geom_bar()
  </code></pre>
  
  <p>I also want to know how to change the legend title and show percentage figures on the graph.</p>