ggplot2: Plotting Andrews curves-CodePudding

I am trying to learn about Andrews plots by doing. I know R has the andrews package that uses the base plotting system, but I wanted to use ggplot2. I followed the

group=Row produces one line in the plot for each row of the data frame. colour=Species colours each line according to the corresponding value of Species.

[There's probably a neater way than uncount() %>% add_column() of replicating each row of iris for each value of t using expand(), but I couldn't get it to work.]

CodePudding user response：

Seems to me that the oversight is that matrices in R are column-major and in python are row-major. In addition, you had hard-coded the iris dataset in your df_out specification whereas it was not a formal argument to the function.

library(ggplot2)

andrews <- function(df, class_column, samples=200) {
  t <- seq(-pi, pi, length.out = samples) 
  
  vals <- t(
    data.matrix(                    
      df[, -which(names(df) %in% class_column)]
    )
  )
  
  curves <- outer(vals[1, ], rep(1, length(t))) 
  
  for (i in 2:nrow(vals)) {                       
    ft = (i %/% 2) * t                          
    if (i %% 2 == 0) {                                
      curves <- curves   outer(vals[i, ], sin(ft))
    } else {
      curves <- curves   outer(vals[i, ], cos(ft))
    }  
  }
  
  row <- as.vector(row(curves))
  col <- as.vector(col(curves))
  
  df_out <- data.frame(
    t = col,
    sample = row,
    values = as.vector(curves),
    class_column = df[[class_column]][row]
  )
  
  df_out 
} 

df <- andrews(iris, "Species")

ggplot(df, aes(x = t, y = values, color = class_column, 
               group = sample))     
  geom_line()

^{Created on 2022-01-26 by the reprex package (v2.0.1)}