R中的IF语句 满足条件时在新列中添加新元素

Question

I'm trying to add a column in the data frame where the new element in the new column has the value of "1" if the conditions are met for that particular row.

To check the condition I am iterating through another reference data frame.

county_list = (df$county_name[df$wolves_present_in_county==1 & df$year==2015])

for (i in df$county_name) {
  for (j in county_list) {
    if (df$county_name[i]==county_list[j])
    {
      df$wolvein2015 = 1
      break
    }
  }
}

Error in Output Dataset

Answer 1

Here is an option with dplyr

library(dplyr)
df %>%
     mutate(wolvein2015 = +((year == 2015 & !is.na(year)) &  
         as.logical(wolves_present_in_county) & !is.na(wolves_present_in_county)))

Answer 2

I think you can do what you want in base R. Here is an example using mtcars:

cars <- mtcars
cars$new <- ifelse(cars$cyl == 4 & cars$mpg > 30, 1, 0)

The new column is added with 0/1's based on conditions of 2 other variables.

BTW, because R is a vectorized paradigm, you should only use for loops as a last resort.