How to group by dependent variable?

Question

bargraph from sciplot allows us to plot bar chart with error bars. It also allows grouping by independent variables (factors). I want to group by dependent variable, how can I achieve that

bargraph.CI(x.factor, response, group=NULL, split=FALSE,
col=NULL, angle=NULL, density=NULL,
lc=TRUE, uc=TRUE, legend=FALSE, ncol=1,
leg.lab=NULL, x.leg=NULL, y.leg=NULL, cex.leg=1,
bty="n", bg="white", space=if(split) c(-1,1),
err.width=if(length(levels(as.factor(x.factor)))>10) 0 else .1,
err.col="black", err.lty=1,
fun = function(x) mean(x, na.rm=TRUE),
ci.fun= function(x) c(fun(x)-se(x), fun(x)+se(x)),
ylim=NULL, xpd=FALSE, data=NULL, subset=NULL, ...)

The specification of bargraph.CI is shown above. The response variable is usually numerical vector. This time, I really want to plot three response variables (A,B,C) against the same independent variables. Let me use the data frame "mpg" to illustrate the problem. I can sucessufully get a plot with the following code, here the DV is hwy

data(mpg)
attach(mpg)

bargraph.CI(
class,  #categorical factor for the x-axis
hwy,    #numerical DV for the y-axis
group=NULL,   #grouping factor
legend=T, 
ylab="Highway MPG",
xlab="Class")

I can also successfully get a plot with the only change being the DV (changed from hwy to cty)

data(mpg)
attach(mpg)

bargraph.CI(
class,  #categorical factor for the x-axis
cty,    #numerical DV for the y-axis
group=NULL,   #grouping factor
legend=T, 
ylab="Highway MPG",
xlab="Class")

However, if I want to use the two DVs at the same time, I mean, for each group, I want to display two bars, one for cty and one for hwy.

data(mpg)
attach(mpg)

bargraph.CI(
class,  #categorical factor for the x-axis
c(cty,hwy),    #numerical DV for the y-axis
group=NULL,   #grouping factor
legend=T, 
ylab="Highway MPG",
xlab="Class")

it won't work because of mismatched dimension. How can I achieve this? Well, actually similar effect of bargraph can be achieved by using the method from Boxplot schmoxplot: How to plot means and standard errors conditioned by a factor in R? with ggplot2. So if you have any idea of how to do it with ggplot2, it's also fine for me.

shadow shadow · Accepted Answer · 2013-10-21T15:46:53

As happens often when displaying data, you should manipulate the data first and then use bargraph.CI. In your expamle, the data.frame that you would like to visualize is the following:

df <- data.frame(class=c(mpg$class, mpg$class), 
                 value=c(mpg$cty, mpg$hwy), 
                 grp=rep(c("cty", "hwy"), each=nrow(mpg)))

Then you can use bargraph.CI on this new data.frame.

bargraph.CI(
  class,        #categorical factor for the x-axis
  value,        #numerical DV for the y-axis
  group=grp,    #grouping factor
  data=df, 
  legend=T, 
  ylab="Highway MPG",
  xlab="Class")

How to group by dependent variable?

1 Answers