ifelse 在突变 function 在 r

Question

I am trying to add a column with a condition using the mutate function in r, but keep getting an error. The code is straight from the teacher's lecture, but yet an error occurs. The LineItem column is a factor class, I am not sure if that make a difference. Please advice on what I am missing.

Thank you, Avi

df <- read.csv('ities_short.csv')

colSums(is.na(df))

sl <- str_length(df$LineItem)
avg <- mean(str_length(df$LineItem))

df <- df %>% mutate(LineItem_LongName = ifelse(sl > avg), 1, 0)

Error in ifelse(sl > avg): argument "yes" is missing, with no default

Answer 1

You have placed ')' at wrong places. The general syntax for ifelse is: ifelse(cond,value if true, value if false)

df <- read.csv('ities_short.csv')

colSums(is.na(df))

sl <- str_length(df$LineItem)
avg <- mean(str_length(df$LineItem))

df <- df %>% mutate(LineItem_LongName = ifelse(sl > avg, 1, 0))

Answer 2

@Nirbhay Singh answer is correct. However, if you compare two vectors, it's generally better to use dplyr::if_else because it is stricter regarding NA values:

df <- df %>% mutate(LineItem_LongName = if_else(sl > avg, 1, 0))

See the doc

Answer 3

Don't create separate objects and use it in dataframe, instead keep them in dataframe itself. You can remove the columns later which you don't need. Moreover, you can do this without ifelse .

library(dplyr)
library(stringr)

df %>%
   mutate(temp = str_length(LineItem), 
          LineItem_LongName = as.integer(temp > mean(temp)))

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Or in base R:

df$temp <- nchar(df$LineItem)
transform(df, LineItem_LongName = +(temp > mean(temp)))