I have the following database:
id x
1 2
1 3
2 3
3 3
3 3
3 3
I wanted to create a new database without repeating the value of the field id , to solve this I can average the values of field x that belongs to the same id .
My question is: How can I do this in R ?
There are several ways to do this in R, what you want is to add a variable using another as a group. This SOpt question speaks exactly to this and will help you (#).
But giving an answer to your specific case, different from the molx response.
Rebuilding data:
dados <- read.table(text = "
id x
1 2
1 3
2 3
3 3
3 3
3 3", header = TRUE)
Using data.table :
library(data.table)
dados <- data.table(dados)
dados[ , list(x = mean(x)), by = id]
id x
1: 1 2.5
2: 2 3.0
3: 3 3.0
You can do in base with the function aggregate :
df <- data.frame(id=c(1, 1, 2, 2, 3, 3), x=c(2, 3, 3, 3, 3, 3))
aggregate(x~id, df, FUN=mean)
# id x
#1 1 2.5
#2 2 3.0
#3 3 3.0
With dplyr (a very useful package for manipulating dataframes):
library(dplyr)
df %>% group_by(id) %>% summarise(x=mean(x))
#mesmo resultado