Center text layer in ggplot barchart

Question

I have a histogram with some text and I m trying to center it for the corresponding type

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 %>%
  mutate(type = factor(type, levels = c("inter",  "VIIT", "HIIT"))) %>%
  group_by(year) %>%
  mutate(ratio = amount/sum(amount),
         pos=cumsum(ratio)-ratio/2) %>%
  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()

My plot look like :

Can you help me to solve this problem because I have no idea how to fix it with the position parameter

Thanks

Answer 1

I'm not sure exactly what you're trying to do, but assume that you want the text in the middle of each colored segment of the bar to

1. be in in the center of the bar; and
2. be for a meaningful number showing the size of the bar

To fix the first issue, you need to have the data sorted by type before you calculate the pos value via cumsum.

To fix the second, you should be showing ratio to the label aesthetic, not pos, which is not a meaningful number other than being the horizontal coordinate to place the label.

df %>%
  mutate(type = factor(type, levels = c("inter",  "VIIT", "HIIT"))) %>%
  group_by(year) %>%
  arrange(desc(type)) %>%
  mutate(ratio = amount / sum(amount),
         pos = cumsum(ratio) - ratio / 2) %>%
  ggplot(aes(x = factor(year), y = ratio, fill = type)) +
  geom_bar(stat = "identity") +
  geom_text(aes(y = pos, label = percent(ratio)), size = 4) +
  scale_y_continuous(name="", labels = percent) +
  coord_flip()

By the way, this isn't a histogram, it's a stacked filled bar chart. A histogram is something quite different.

Edit - alternative, easier method

As pointed out in the comments, the fairly recent addition to ggplot2, position_stack, will calculate the position for you rather than creating pos variable in your data pipeline. So the code below is perhaps a neater way of doing the whole thing (gives identical result):

df %>%
  group_by(year) %>%
  mutate(type = factor(type, levels = c("inter",  "VIIT", "HIIT"))) %>%
  mutate(ratio = amount / sum(amount)) %>%
  ggplot(aes(x = factor(year), y = ratio, fill = type)) +
  geom_bar(stat = "identity") +
  geom_text(aes(label = percent(ratio)), position = position_stack(vjust = 0.5), size = 4) +
  scale_y_continuous(name="", labels = percent) +
  coord_flip()