A efficient implementation of cosine similarity created for a Shiny app about games.

cosine_similarity_vectorized.R

cosine_similarity_vec <- function(row_index, df){
  row <- df[row_index,]
  mat <- df[-row_index,]
  numerator <- rowSums(sweep(mat, MARGIN=2, row, "*"))
  denominator <- sqrt(sum(row**2)) * sqrt(rowSums(mat**2))
  similarities <- numerator/denominator
  game_numbers <- 1:dim(df)[1]
  game_numbers <- game_numbers[! game_numbers %in% row_index]
  df_similarity <- data.frame(game_numbers, similarities)
  df_similarity <- df_similarity %>% arrange(desc(similarities))
  return(df_similarity)
}