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geom_bar with missing data in package ggplot

3 messages · Dennis Murphy, Aidan Corcoran

Aidan Corcoran
# 
Dear all,

I was hoping someone could help with a ggplot question. I would like
to generate a faceted bar chart, but missing data are causing
problems.

g<-structure(list(Date = structure(c(11322, 11687, 12052, 11322,
11687, 12052, 11322, 11687, 12052, 11322, 11687, 12052), class = "Date"),
    variable = c("Govt Revenues to GDP", "Govt Revenues to GDP",
    "Govt Revenues to GDP", "Govt Revenues to GDP", "Govt Revenues to GDP",
    "Govt Revenues to GDP", "Structural Budget Position", "Structural
Budget Position",
    "Structural Budget Position", "Structural Budget Position",
    "Structural Budget Position", "Structural Budget Position"
    ), var2 = c("United States", "United States", "United States",
    "Japan", "Japan", "Japan", "United States", "United States",
    "United States", "Japan", "Japan", "Japan"), value = c(NA,
    34.288, 31.831, 29.636, 30.539, 29.093, NA, 0, -2.7, -7.4,
    -5.7, -7)), .Names = c("Date", "variable", "var2", "value"
), row.names = c(21L, 22L, 23L, 169L, 170L, 171L, 206L, 207L,
208L, 354L, 355L, 356L), class = "data.frame")

gp <- ggplot(g, aes(Date, value))
gp<- gp + geom_line()
gp <-gp + facet_grid(var2 ~ variable)
gp

this works, but trying to get a bar chart version

gp <- ggplot(g, aes(Date, value))
gp<- gp + geom_bar(stat="identity")
gp <-gp + facet_grid(var2 ~ variable)
gp

gives the error
Error in if (!is.null(data$ymin) && !all(data$ymin == 0))
warning("Stacking not well defined when ymin != 0",  :
  missing value where TRUE/FALSE needed

Is there something I can do to have a gap for missing data, as happens
with the line version?

More generally, I may also have missing data between present data: e.g.

is.na(g[5,4])<-TRUE

and I would like if possible to simply see gaps at these points.

Thanks for any help.

Aidan
Dennis Murphy
# 
Hi:

Here's one way, but it puts the two countries side by side rather than
stacked (I'm not a big fan of stacked bar charts except in certain
contexts). The first version uses the original data, but one can see
immediately that there is no distinction between NA and 0:

ggplot(g, aes(x = Date, y = value, fill = var2)) +
    geom_bar(position = 'dodge', stat = 'identity') +
    facet_wrap(~ variable, nrow = 1) +
    scale_fill_manual('Country', breaks = levels(g$var2),
                                 values = c('red', 'blue')) +
    opts(legend.position = c(0.87, 0.88),
         legend.background = theme_rect(fill = 'white'))

To compensate, I copied the data to a new object g2 and imputed a
small negative value to replace the zero:

g2 <- g
g2$value[8] <- -0.01
ggplot(g2, aes(x = Date, y = value, fill = var2)) +
    geom_bar(position = 'dodge', stat = 'identity') +
    facet_wrap(~ variable, nrow = 1) +
    scale_fill_manual('Country', breaks = levels(g2$var2),
                                 values = c('red', 'blue')) +
    opts(legend.position = c(0.87, 0.88),
         legend.background = theme_rect(fill = 'white'))

An additional improvement could be made by keeping the original data
and adding some text that indicates where the NAs reside; to do this,
we need to offset the date a bit to decently locate the text:

ggplot(g, aes(x = Date, y = value, fill = var2)) +
    geom_bar(position = 'dodge', stat = 'identity') +
    facet_wrap(~ variable, nrow = 1) +
    scale_fill_manual('Country', breaks = levels(g$var2),
                                 values = c('red', 'blue')) +
    geom_text(aes(x = as.Date('2001-3-31'), y = 1, label = 'NA'),
               size = 6) +
    opts(legend.position = c(0.87, 0.88),
         legend.background = theme_rect(fill = 'white'))

HTH,
Dennis



On Wed, Nov 16, 2011 at 1:55 AM, Aidan Corcoran
<aidan.corcoran11 at gmail.com> wrote:
Aidan Corcoran
# 
Hi Dennis,

that does exactly what I needed, and the treatment of missing values
is really useful.

thanks for your help.
Aidan
On Wed, Nov 16, 2011 at 12:22 PM, Dennis Murphy <djmuser at gmail.com> wrote: