Creating a Bar Plot with Multiple Independent Variables in One Plot

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In this article, we will explore the process of creating a bar plot that includes multiple independent variables in one plot. We will use the popular R package ggplot2 to achieve this.

Introduction

When working with multiple independent variables, it can be challenging to visualize them all on a single plot. However, there are several techniques we can use to create a plot that effectively represents multiple variables.

One common technique is to use a bar plot with separate bars for each category of the independent variable(s). This approach works well when we have a limited number of categories. However, as the number of categories increases, this approach can become cluttered and difficult to interpret.

Dodge Plot

Another approach to create a bar plot with multiple independent variables is to use a dodge plot. A dodge plot is a type of bar plot that allows us to position bars in different ways along the same axis. This approach works well when we have multiple independent variables, each with its own set of categories.

In the original question, the user wants to create a bar plot where the IV emotionality is added as emotional or neutral bars. This can be achieved using a dodge plot, where the emotional and neutral bars are positioned in different ways along the x-axis.

Setting Up the Data

To demonstrate this technique, let’s set up our data. We will use a sample dataset with four independent variables: Training_Task, emotionality, target_type, and acc.

Training_Task <- c("Imag", "Imag", "Imag", "Imag", "Rephrasing", "Rephrasing", "Rephrasing", "Rephrasing")
emotionality <- c("emo", "neu", "emo", "neu", "emo", "neu", "emo", "neu")
target_type <- c("novel", "novel", "pseudo", "pseudo", "novel", "novel", "pseudo", "pseudo")
acc <- c(93, 95, 97, 98, 96, 94, 92, 90)
df <- data.frame(Training_Task, emotionality, target_type, acc)

Creating the Bar Plot

To create the bar plot, we will use the ggplot2 package. We will set up a dodge plot by specifying the position parameter as “dodge”.

ggplot(df) +
  geom_bar(aes(fill = Training_Task, y=acc, x=target_type, alpha = emotionality), stat = 'identity', 
          position = "dodge") +
  theme_minimal() +
  scale_alpha_discrete(range = c(1,0.4))

In this code:

• We create a new ggplot object by calling ggplot(df).
• We specify the aesthetic mappings using the aes() function.
  • fill maps the Training_Task variable to the fill color of the bars.
  • y maps the acc variable to the height of the bars.
  • x maps the target_type variable to the position of the bars along the x-axis. We set the position parameter as “dodge” to allow for different positions of the bars.
  • alpha maps the emotionality variable to the transparency of the emotional and neutral bars.
• We specify the theme using the theme_minimal() function.
• We scale the alpha values from 1 (fully opaque) to 0.4 (partially transparent).

Positioning Bars in a Dodge Plot

To position bars in a dodge plot, we can use different positions for each category of the independent variable(s). In our example, we want to position the emotional and neutral bars in different ways along the x-axis.

ggplot(df) +
  geom_bar(aes(fill = Training_Task, y=acc, x=target_type, position = emotionality), stat = 'identity') +
  theme_minimal() +
  scale_fill_discrete(name="Emotionality") +
  scale_x_continuous(breaks = c("novel", "pseudo"), labels = function(x) {ifelse(x == "novel", "Novel", "Pseudo")})

In this code:

• We specify the position parameter as a function of the emotionality variable.
  • For emotional categories ( emo), we want to position them at the left edge of the plot, where novel targets are placed.
  • For neutral categories (neu), we want to position them at the right edge of the plot, where pseudo targets are placed.
• We scale the x-axis using scale_x_continuous(), specifying breaks and labels for each category.

Conclusion

In this article, we demonstrated how to create a bar plot with multiple independent variables in one plot using ggplot2. We discussed the use of dodge plots to position bars along the same axis and used examples to illustrate the technique.

Last modified on 2025-04-29