How to create "back-to-back" bar chart

[Greg Blevins]

df <- structure(list(q9_1recodet = c(1, 0, 1, 1, 0, 0, 0, 0, 0, 0,
0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1), q9_2recodet = c(1,
0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1,
0, 0, 0, 0, 1), q9_3recodet = c(1, 0, 1, 0, 0, 0, 0, 0, 0, 0,
0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1)), .Names =
c("q9_1recodet",
"q9_2recodet", "q9_3recodet"), row.names = c(1L, 2L, 3L, 4L,
5L, 6L, 8L, 9L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L, 19L,
20L, 22L, 23L, 24L, 25L, 26L, 27L, 28L, 29L, 30L), class =
"data.frame", na.action = structure(c(7L, 10L, 21L), .Names = c("7", "10",
"21"), class = "omit"))

I would like to create a graph similar to the image shown here -- this type
of graph is frequently used by the Pew Research center.

<Loading Image...>


I manipulate the data as follows to get summary measures:

df <- melt(df)
a <- with(df, ftable(xtabs(~ value + variable)))
a <- round(prop.table(a,2) * 100, 0)
a <- as.data.frame(a)

My summary data looks like this:

value variable Freq
1 0 q9_1recodet 78
2 1 q9_1recodet 22
3 0 q9_2recodet 74
4 1 q9_2recodet 26
5 0 q9_3recodet 67
6 1 q9_3recodet 33
g2 <- ggplot(a, aes( x = variable, y = Freq, fill = value, width=0.9)) +
geom_bar(stat ="identity", position ="dodge") +
geom_text(aes(label = Freq), vjust = -0.4, colour ="black", position =
position_dodge(.9), size = 4)
g2 + coord_cartesian(ylim = c(1,100))

<Loading Image...>
But, at this point I am stumped on how to proceed to generate a
"back-to-back" bar plot like the Pew example shown above. Hence, I would
like the light blue bars in the bar chart above to display to the right and
the red bars to display to the left. Any help would be much appreciated.

Thanks,

Greg
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[Stuart Luppescu]

Post by Greg Blevins
I am stumped on how to proceed to generate a
"back-to-back" bar plot like the Pew example shown above. Hence, I
would like the light blue bars in the bar chart above to display to
the right and the red bars to display to the left. Any help would be
much appreciated.

I had a similar problem a week or so ago. I wanted to center bars at a
certain point. The solution is to separate the data set into two and
multiply one subset by -1. Then use two geom_bar() statements. Here is
some of the code I used (I'm sure you can modify it to get it to do what
you want):

ggplot(testratings[testratings$rating>=3,], aes(x=fake.schlid,
y=percent, fill=rating.c)) +
geom_bar(stat="identity") +
scale_y_continuous(name="Percentage", limits=c(-100, 100)) +
geom_bar(data=testratings[testratings$rating<3,], aes(x=fake.schlid,
y=(-1)*percent, fill=rating.c), stat="identity") +
theme(axis.text.x = element_text(angle = 90, hjust = 1)) +
scale_fill_manual(name="Rating", values=rev(mypal)) +
labs(title="Percentages of Ratings by School", x="School ID")
--
Stuart Luppescu <slu-XTq9FdIHtvQ2LMHL4Co/***@public.gmane.org>
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