Using ifelse to transform column in R

Question

I have a dataframe with a column of numbers.

In a separate column, I want to print whether the number is \"less than 10\", \"between 10 and 20\" or \"between 20 and 30\

Answer 1

You could use cut from base R, but be aware it makes the words variable a factor. You just need to set the appropriate intervals (which is why I used 30.5 etc for readibility). BTW, in your example you coded 20 should be recoded both to "between 10 and 20" and to "between 20 and 30", which won't work.

data$words <- cut(data$number, c(0,9.5,20.5,30.5,40), c("less than 10", "between 10 and 20", "between 20 and 30", "other"))
data

Answer 2

The main problem was that you need to reference the variable in each inequality test. To make this more readable, I wrapped everything in a with(data... call. Another problem with your code was the use of && instead of &. The former is for single values only while the latter compares each element of two vectors.

data$words<-
  with(data,
       ifelse(number >= 0 & number <= 9, "less than 10",
       ifelse(number >= 10 & number <= 20, "between 10 and 20",
       ifelse(number >= 20 & number <= 30, "between 20 and 30", "other"))))

I also think this is a lot more readable than the tidyverse without introducing new syntax. It is easier to debug, too.

Answer 3

library(tidyverse)
 data<-data.frame(number=(1:40))
 data %>% 
   mutate(word = case_when(
     number>=0 & number<10~"less than 10",
     number>=10 & number<20~"between 10 and 20",
     number>=20 & number<30~"between 20 and 30",
     T~"Other"
   ))
   number              word
1       1      less than 10
2       2      less than 10
3       3      less than 10
4       4      less than 10
5       5      less than 10
6       6      less than 10
7       7      less than 10
8       8      less than 10
9       9      less than 10
10     10 between 10 and 20
11     11 between 10 and 20
12     12 between 10 and 20
13     13 between 10 and 20
14     14 between 10 and 20
15     15 between 10 and 20
16     16 between 10 and 20
17     17 between 10 and 20
18     18 between 10 and 20
19     19 between 10 and 20
20     20 between 20 and 30
21     21 between 20 and 30
22     22 between 20 and 30
23     23 between 20 and 30
24     24 between 20 and 30
25     25 between 20 and 30
26     26 between 20 and 30
27     27 between 20 and 30
28     28 between 20 and 30
29     29 between 20 and 30
30     30             Other
31     31             Other
32     32             Other
33     33             Other
34     34             Other
35     35             Other
36     36             Other
37     37             Other
38     38             Other
39     39             Other
40     40             Other

Answer 4

do you need it to be all in one statement?

There are a few syntactical mistakes in your code, but a possible solution would be to do something like this

data$text <- "other"
data$text[data$number >=0 & data$number < 10] <- "less than 10"
data$text[data$number >=10 & data$number < 20] <- "between 10 and 20"
data$text[data$number >=20 & data$number < 30] <- "between 20 and 30"

I created a new column because if I were to replace the values in the 'number' column with text, the entire column would be coerced to character type and it might cause unexpected behaviour with the inequality operators.

You also have some overlap in your categories. Consider changing your upper bound to strictly less than (for example 20 is both >=20 and <=20, so falls into the "between 10 and 20" and "between 20 and 30" categories

If you want a one-liner, you can use the cut() function:

cut(data$number, breaks=c(0,10,20,30,Inf), 
labels=c("less than 10", "between 10 and 20", "between 20 and 30", "other"))

this turns a numeric vector into factor.