Position Dodge with geom_point(), x=continuous, y=factor

Introduction

In this article, we will explore how to use position dodge in ggplot2 to achieve a specific layout for our plots. We will delve into the details of how position dodge works and provide examples of its usage.

Understanding Position Dodge

Position dodge is a geom_point function argument used to control the positioning of points on the plot. When used with geom_point, it adjusts the x or y coordinates (or both) of the points in order to prevent overlapping.

There are different ways to position dodge: sideways, vertically, horizontally, and diagonally. However, when using geom_point with a continuous variable as the x-axis (x=continuous) and a factor as the y-axis (y=factor), we can only use positional dodging that affects either the x or y axis.

Using Position Dodge

The position dodge function takes one argument: width for sideways positioning, which controls how much space is between points. The default width value is 0.5.

When you try to use position dodge in your plot with a continuous variable as x and a factor as y, the points will appear dodged on the specified axis. This works by reversing the order of the data, using reorder_by function before specifying position_dodge, then flipping the plot back.

Here is an example code snippet:

library(pacman)
p_load(devtools, psych, stringr, plotflow)
source_url("https://raw.githubusercontent.com/Deleetdk/psych2/master/psych2.R")

loadings.plot2 = function(fa.objects, fa.names=NA) {
  fa.num = length(fa.objects) #number of fas

  #check names are correct or set automatically
  if (length(fa.names)==1 &amp; is.na(fa.names)) {
    fa.names = str_c("fa.", 1:fa.num)
  }
  if (length(fa.names) != fa.num) {
    stop("Names vector does not match the number of factor analyses.")
  }

  #merge into df
  d = data.frame() #to merge into
  for (fa.idx in 1:fa.num) { #loop over fa objects
    loads = fa.objects[[fa.idx]]$loadings
    rnames = rownames(loads)
    loads = as.data.frame(as.vector(loads))
    rownames(loads) = rnames
    colnames(loads) = fa.names[fa.idx]

    d = merge.datasets(d, loads, 1)
  }

  #reshape to long form
  d2 = reshape(d,
               varying = 1:fa.num,
               direction="long",
               ids = rownames(d))
  d2$time = as.factor(d2$time)
  d2.id = as.factor(d2.id)
  colnames(d2)[2] = "fa"

  print(d2)

  #plot
  g = ggplot(reorder_by(id, ~ fa, d2), aes(x=id, y=fa, color=time, group=time)) +
      geom_point(position=position_dodge(width = .5)) +
      xlab("Loading") + ylab("Indicator") +
      scale_color_discrete(name="Analysis",
                           labels=fa.names) +
      coord_flip()

  return(g)
}

#Some example plots    
fa1 = fa(iris[-5])
fa2 = fa(iris[-c(1:50),-5])
fa3 = fa(ability)
fa4 = fa(ability[1:50,])

loadings.plot2(list(fa1,fa1,fa2))

Conclusion

In conclusion, position dodge is a powerful tool in ggplot2 for positioning points on the plot. By using positional dodging that affects either the x or y axis and reversing the order of the data before specifying position_dodge, we can achieve the desired layout.

Troubleshooting Position Dodge with Geom Point

No Points Appearing Due to Overlap

When you use geom_point and position dodge, but no points appear due to overlap, there are a few possible solutions:

Increase the width value: Increase the width value in position_dodge() function for sideways positioning. This will increase the space between the points.

g = ggplot(reorder_by(id, ~ fa, d2), aes(x=id, y=fa, color=time, group=time)) + geom_point(position=position_dodge(width = .5)) +


*   **Decrease the number of data points**: Decreasing the number of data points may help prevent overlapping. Consider using a subset of the data.
    ```markdown
  g = ggplot(reorder_by(id, ~ fa, d2), aes(x=id, y=fa, color=time, group=time)) +
      geom_point(data=d2)

Use coord_flip(): If you’re having trouble with points overlapping, try using coord_flip() function to reverse the plot.

g = ggplot(reorder_by(id, ~ fa, d2), aes(x=id, y=fa, color=time, group=time)) + geom_point(position=position_dodge(width = .5)) + xlab(“Loading”) + ylab(“Indicator”) + scale_color_discrete(name=“Analysis”, labels=fa.names) + coord_flip()


*   **Use facet_grid()**: If you're having trouble with points overlapping, try using `facet_grid()` function to separate the data into multiple subplots.
    ```markdown
  g = ggplot(reorder_by(id, ~ fa, d2), aes(x=id, y=fa, color=time, group=time)) +
      geom_point(position=position_dodge(width = .5)) +
      facet_grid(~ fa)

Additional Tips

Use position_dodge with caution: Position dodge can lead to uneven spacing of points. Make sure the data is in the correct order and that there are no duplicate values.
Consider using coord_equal instead: If you’re having trouble with position dodge, consider using coord_equal() function instead, which maintains equal aspect ratios across all layers.

By following these tips and understanding how position dodge works, you can create plots with neatly positioned points.

Last modified on 2024-11-21