CODEWITHSUNDEEP
r
Duck
Duck

Reputation: 39613

Replace the value in a row when two columns have specific values

I am lloking for a solution to this problem in R. I have a data frame like this:

A1 A2 A3 A4
22  a  1  1
22  b  3  3
21  c  1  2
23  w  1  1
22  a  4  4

I look for a way to change the values in A1 column when A1 and A2 have a value of 22 and a. In this case when this cristeris is gotten A1 will have a value of 19, and the data frame will be like this:

A1 A2 A3 A4
19  a  1  1
22  b  3  3
21  c  1  2
23  w  1  1
19  a  4  4

Upvotes: 1

Views: 186

Answers (2)

user2627717
user2627717

Reputation: 344

If you have large data tables, and speed matters, I would recommend data.table. Here is what it would look like.

library(data.table)
example <- data.table(example)
setkey(example,A1,A2)
example[J(22,"a"), A1 := 19] #uses binary search, faster than example[A1 ==22 & A2 == "a", A1 := 19]

> example
    A1 A2 A3 A4
1: 19  a  1  1
2: 22  b  3  3
3: 21  c  1  2
4: 23  w  1  1
5: 19  a  4  4

Feel free to compare times for the data.frame and data.table solutions on a larger data set.

Upvotes: 2

dayne
dayne

Reputation: 7794

example <- data.frame(A1=c(22,22,21,23,22),A2=c("a","b","c","w","a"),A3=c(1,3,1,1,4),A4=c(1,3,2,1,4))

example$A1[example$A1==22 & example$A2=="a"] <- 19

> example
  A1 A2 A3 A4
1 19  a  1  1
2 22  b  3  3
3 21  c  1  2
4 23  w  1  1
5 19  a  4  4

Upvotes: 1

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