Adding new column with conditional values using ifelse

Question

I have a data frame with more than 400.000 observations and I'm trying to add a column to it which its values depend on another column and sometimes multiple ones.

Here is a simpler example of what I'm trying to do :

# Creating a data frame 

M <- data.frame(c("A","B","C"),c(5,100,60))

names(M) <- c("Letter","Number")

#adding a column 

M$Size <- NA

# if Number <= 50 Size is small, 
# if Number is between 50 and 70, Size is Medium
# if Number is Bigger than 70, Size is Big

ifelse (M$Number <=50, M$Size <-"Small",
        ifelse(M$Number <= 70,
        M$Size <- "Medium",
        M$Size <- "Big"
        ))

When I run the Code, the output I get is :

[1] "Small"  "Big"    "Medium"

But the "Size" column in M is always the last condition in the ifelse function :

> print (M)
  Letter Number Size
1      A      5  Big
2      B    100  Big
3      C     60  Big

The Result that I want :

> print (M)
  Letter Number Size
1      A      5  Small
2      B    100  Big
3      C     60  Medium

I can solve the problem by subsetting each conditionsubset and using rbind to get the result I want but the code will be very long and since the original data frame I'm working on is big, it'll take more time to run. So I'm wondering how can I fix this issue ?

cut(M[, 2], c(-Inf, 50,70, Inf), c("Small", "Medium", "Big")) — JACKY88
– JACKY88, Commented May 19, 2016 at 10:56

PRYM · Accepted Answer · 2016-05-19 11:17:05Z

13

This will help you out -

# Creating a data frame 

M <- data.frame(c("A","B","C"),c(5,100,60))

names(M) <- c("Letter","Number")

#adding a column 


# if Number <= 50 Size is small, 
# if Number is between 50 and 70, Size is Medium
# if Number is Bigger than 70, Size is Big

# M$Size[M$Number <= 50] <- "Small"
# Edit: No need to subset "Small"
M$Size <- "Small"
M$Size[M$Number >50 & M$Number<70] <- "Medium"
M$Size[M$Number > 70] <- "Big"

#      Letter Number   Size
# 1      A      5      Small
# 2      B    100      Big
# 3      C     60      Medium

See this on R-Fiddle

edited May 19, 2016 at 11:17

answered May 19, 2016 at 10:57

PRYM

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2 Comments

Roland Over a year ago

This is better than using ifelse. Have an upvote. However, you don't need the subsetting in the first step if there are no NA values. Just do M$Size <- "Small".

PRYM Over a year ago

@Roland Yes you are right, I oversaw that. Will edit

Roland · Accepted Answer · 2016-05-19 10:55:34Z

10

Use cut:

M$Size <- cut(M$Number, breaks = c(-Inf, 50, 70, Inf), 
                        labels = c("small", "medium", "large"))
#   etter Number   Size
#1      A      5  small
#2      B    100  large
#3      C     60 medium

answered May 19, 2016 at 10:55

Roland

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Comments

elevendollar · Accepted Answer · 2016-05-19 10:58:32Z

6

Same idea but assign it like this instead. No package needed.

M$Size <- ifelse(M$Number <= 50, 'Small', ifelse(M$Number <= 70, 'Medium', 'Big'))

Result:

  Letter Number   Size
1      A      5  Small
2      B    100    Big
3      C     60 Medium

answered May 19, 2016 at 10:58

elevendollar

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Comments

user2110417 · Accepted Answer · 2023-07-10 09:25:52Z

0

You can also try

df <- data.frame(c("A","B","C"),c(5,100,60))
names(df) <- c("Letter","Number")

df$Size = with(df,
               ifelse(Number <= 50, 'Small',
                     ifelse(Number > 50 & Number < 70, 'Medium',
                           ifelse(Number > 70, 'Big', 'NA'))))

answered Jul 10, 2023 at 9:25

user2110417

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