Update battery_deltas.R to handle empty dataframes

src/features/battery_deltas.R

@@ -4,6 +4,7 @@ library("tidyverse")
 
 battery <- read.csv(snakemake@input[[1]])
 
+if(nrow(battery) > 0){
   consumption <- battery %>%
     mutate(group = ifelse(lag(battery_status) != battery_status, 1, 0) %>% coalesce(0),
            group_id = cumsum(group) + 1) %>%
@@ -17,5 +18,13 @@ consumption <- battery %>%
               local_end_date = last(local_date)) %>%
     select(-group_id) %>%
     filter(time_diff > 0.1) # Avoids including quick cycles
+} else {
+  consumption <- data.frame(battery_diff = numeric(), 
+                            time_diff = numeric(),
+                            local_start_date_time = character(),
+                            local_end_date_time = character(),
+                            local_start_date = character(),
+                            local_end_date = character())
+}
 
 write.csv(consumption, snakemake@output[[1]], row.names = FALSE)