Q:

geom_histogram does not show all values in x axis

Trying to run a simple and quick analysis of some variables. I run this code:
ggplot(data, aes(var1)) +
    geom_bar()

Resulting in a Histogram however in spite of having only 6 possible values in var1, x Axis only shows 2,4,6. Is it possible to easily include all 6 possible values as labels? 

A:

You want to have frequency bar plot for six individual numbers. However, you wish to see all of these numbers on the X axis, which makes me think that you actually treat them as categorical data rather then numeric data, so you actually would prefer a categorical X axis which shows all the data. Turning the x into a factor should do the trick:
data <- data.frame(var1=floor(6*runif(200)  + 1))
ggplot(data, aes(factor(var1))) + geom_bar()

Below: left - without factor, right - with factor.

