Creating a Function with For Loop and If Else-CodePudding

Hi I am supposed to create a function 'check_even' that accepts three arguments (1) ' df' a dataframe (2) ' col_test' to test if each row value in the indicated column is even or odd. Use for loop and nrow function. (3) ' col_multiply' the column to multiply by 2 if the 'col_test' is even and multiply by 3 if the 'col_test' is odd

Store the result in a new column in the ' df' call ' res' and return the whole dataframe ' df'
Test your function by running this code ' check_even(df_test, 'INT1', 'INT2')'


df_test = data.frame(INT1 = c(1:10), INT2 = (sample(x = c(20:100),size = 10, replace = F)))
df_test

check_even = function(df, col_test, col_multiply){
  for(i in 1:nrow(df)){
    if((df[,col_test[i]] %% 2) == 0){
      df[,'res'] = (df[,col_multiply[i]] * 2)
      
    } else 
      {
        df[,'res'] = (df[,col_multiply[i]] * 3)
        
        } 
    return(df) }
}  

 
check_even(df_test, 'INT1', 'INT2')

I keep getting a result of all the values multiply by 3. Can I seek some help to see what is wrong with my codes?

CodePudding user response：

Try simpler solution with ifelse:

df_test = data.frame(INT1 = c(1:10), INT2 = (sample(x = c(20:100),size = 10, replace = F)))
df_test

check_even = function(df, col_test, col_multiply) {
  for(i in 1:nrow(df)){
    df$res = ifelse(df[,col_test[i]] %% 2 == 0, df[,col_multiply[i]] * 2, df[,col_multiply[i]] * 3)
    return(df)}
}  


check_even(df_test, 'INT1', 'INT2')

CodePudding user response：

You may try

check_even = function(df, col_test, col_multiply){
  res <- c()
  for(i in 1:nrow(df)){
    if((df[i,col_test] %% 2) == 0){
      res = c(res,df[i,col_multiply] * 2)
      
    } else 
    {
      res = c(res,df[i,col_multiply] * 3)
    } 
  }
  df$res <- res
  return(df)
}  



check_even(df_test, 'INT1', 'INT2')

   INT1 INT2 res
1     1   61 183
2     2   88 176
3     3   85 255
4     4   95 190
5     5   81 243
6     6   83 166
7     7   70 210
8     8   37  74
9     9   29  87
10   10   91 182

Or using dplyr, it do not need any for loop

library(dplyr)

check_even = function(df, col_test, col_multiply){
  df %>%
    mutate(res = ifelse({{col_test}} %% 2 == 0, {{col_multiply}} * 2, {{col_multiply}} * 3))
}  
    

check_even(df_test, INT1, INT2)

   INT1 INT2 res
1     1   61 183
2     2   88 176
3     3   85 255
4     4   95 190
5     5   81 243
6     6   83 166
7     7   70 210
8     8   37  74
9     9   29  87
10   10   91 182