Creating a new variable in a data frame and changing its values in one step

Question

I have a column which is part of a data frame, df. It is full of integers. Let's say it is the number of houses sold in a day by a reality compant. Let's call it df$houses. I want to make a second column called df$quant where the number of houses is categorized, with 0 being 0-2 houses sold in a day, 1 being 3-5 houses, 2 being 6-9 houses and 3 being more than 10 houses? I could do this in two steps.

1) Create the new column df$quant from df$houses:

df$quant <- df$houses

2) Change the values of df$quant:

df$quant[which(df$quant <= 2)] <- 0

etc.

I would like to do this in one step though, making the new variable and filling it with the proper values. Mostly, so I don't have to worry about getting the order of the lines of code in the second step right. It would be more robust.

Could this be done with an if statement?

Thanks a lot.

Have a look at `?cut` which would better suit in this case. – Ronak Shah Jul 06 '17 at 13:12 — Ronak Shah, Jul 06 '17 at 13:12

minem · Accepted Answer · 2017-07-06T13:45:15.377

2

I would do something like this: (using cut)

x <- 1:11
df <- data.frame(x)

myFunction <- function(x) as.integer(cut(x, c(-1, 2, 5, 9, max(x)))) - 1
df$new <- myFunction(df$x)
df
    x new
1   1   0
2   2   0
3   3   1
4   4   1
5   5   1
6   6   2
7   7   2
8   8   2
9   9   2
10 10   3
11 11   3

edited Jul 06 '17 at 13:45

answered Jul 06 '17 at 13:16

minem

3,640
2
15
29

1

Might need to change the first break in the cut function from `0` to be either `-1` or `-Inf` to ensure there are no `NA` values if there are zero houses sold. – Matt Jewett Jul 06 '17 at 13:40
This should work. Thanks! – Gregory Anderson Jul 06 '17 at 13:50

Creating a new variable in a data frame and changing its values in one step

1 Answers1