Transformations

The relationship between two variables may not be linear. In these cases we can sometimes see strange and even inscrutable patterns in a scatterplot of the data. Sometimes there really is no meaningful relationship between the two variables. Other times, a careful transformation of one or both of the variables can reveal a clear relationship.

Recall the bizarre pattern that you saw in the scatterplot between brain weight and body weight among mammals in a previous exercise. Can we use transformations to clarify this relationship?

ggplot2 provides several different mechanisms for viewing transformed relationships. The coord_trans() function transforms the coordinates of the plot. Alternatively, the scale_x_log10() and scale_y_log10() functions perform a base-10 log transformation of each axis. Note the differences in the appearance of the axes.

The mammals dataset is available in your workspace.

1
Use coord_trans() to create a scatterplot showing how a mammal's brain weight varies as a function of its body weight, where both the x and y axes are on a "log10" scale.
2
Use scale_x_log10() and scale_y_log10() to achieve the same effect but with different axis labels and grid lines.

Exercise

Transformations

Instructions 1/2