How can I suppress the vertical gridlines in a ggplot2 plot?

Option 1:

data_df <- data.frame(x = 1:10, y = c(3,5,2,5,6,2,7,6,5,4))

ggplot(data_df, aes(x, y)) +
  geom_bar(stat = 'identity') +
  theme(panel.background = element_rect(fill = "white"))

Option 2:

data_df <- data.frame(x = 1:10, y = c(3,5,2,5,6,2,7,6,5,4))
    
ggplot(data_df, aes(x, y)) +
      geom_bar(stat = 'identity') +
      theme(
        panel.grid.major.x = element_blank(),
        panel.grid.minor.x = element_blank(),
        panel.grid.major.y = element_blank(),
        panel.grid.minor.y = element_blank()
      )

Try using

scale_x_continuous(breaks = NULL)

This would remove all the vertical gridlines as well as x-axis tickmark labels.

As of ggplot2 0.9.2, this has become much easier to do using "themes." You can now assign themes separately to panel.grid.major.x and panel.grid.major.y, as demonstrated below.

#   simulate data for the bar graph
data <- data.frame( X = c("A","B","C"), Y = c(1:3) )    

#   make the bar graph
ggplot( data  ) +
    geom_bar( aes( X, Y ) ) +
    theme( # remove the vertical grid lines
           panel.grid.major.x = element_blank() ,
           # explicitly set the horizontal lines (or they will disappear too)
           panel.grid.major.y = element_line( size=.1, color="black" ) 
    )

The result of this example is quite ugly looking, but it demonstrates how to remove the vertical lines while preserving the horizontal lines and x-axis tick-marks.

This leaves you only with the data points:

ggplot(out, aes(X1, X2)) + 
    geom_point() + 
    scale_x_continuous(breaks = NULL) + 
    scale_y_continuous(breaks = NULL) + 
    opts(panel.background = theme_blank()) + 
    opts(axis.title.x = theme_blank(), axis.title.y = theme_blank())