R - Error in summarise_impl(.data, dots) : Column `center` must be length 1 (a summary value), not 2

Question

I'm trying to calculate the center of each group, by running the calc_center function with dplyr's group_by_ and summarise functions. However, I received an error saying that the column must be 1 column not two. What can I do to bypass it? This is my code.

library(dplyr)
library(car)

calc_center <- function(x,y){
  MASS::cov.trob(cbind(x, y)$center
}

results <- data %>%
  group_by(group) %>%
  summarise(center=calc_center(Latitude, Longitude))

This is my error

Error in summarise_impl(.data, dots) : 

Column center must be length 1 (a summary value), not 2

Answer 1

In the future, it'd be nice if you included at least a brief example of your data for troubleshooting/reproducibility purposes.

The issue is likely because you'd like to apply the function to each row for the Latitude and Longitude columns. In this case, using dplyr::rowwise() should solve the issue:

E.g.;

results <- data %>%
  group_by(group) %>%
  rowwise() %>%
  summarise(center=calc_center(Latitude, Longitude)) %>%
  ungroup()

You could also probably get away with using mutate instead of summarise.

Hope that was helpful!