Ala Ala - 1 year ago 74
R Question

Rank observation by a group based on a dynamic variable name

I have a data frame with a group column and several numeric columns. In addition, I have a variable that stores the column name I need to rank observation on. Say this is my data frame

> x = "myValue1"
> set.seed(123)
> df = data.frame(myValue1 = rnorm(9, mean = 10),
myValue2 = rnorm(9, mean = 2),
myGroup = rep(c("a","b","c"), each = 3),
myEntity = paste0("entity",1:9))
> df
myValue1 myValue2 myGroup myEntity
1 9.439524 1.55433803 a entity1
2 9.769823 3.22408180 a entity2
3 11.558708 2.35981383 a entity3
4 10.070508 2.40077145 b entity4
5 10.129288 2.11068272 b entity5
6 11.715065 1.44415887 b entity6
7 10.460916 3.78691314 c entity7
8 8.734939 2.49785048 c entity8
9 9.313147 0.03338284 c entity9


what I want is within each group to return the rank of each observation using the column from
x
(in this case it is
myValue1
). So, I want to return the following data frame

> library(dplyr)
> df = data.frame(df %>%
group_by(myGroup) %>%
mutate(myRank = order(myValue1,myEntity)))
> df
myValue1 myValue2 myGroup myEntity myRank
1 9.439524 1.55433803 a entity1 1
2 9.769823 3.22408180 a entity2 2
3 11.558708 2.35981383 a entity3 3
4 10.070508 2.40077145 b entity4 1
5 10.129288 2.11068272 b entity5 2
6 11.715065 1.44415887 b entity6 3
7 10.460916 3.78691314 c entity7 2
8 8.734939 2.49785048 c entity8 3
9 9.313147 0.03338284 c entity9 1


This was easy because I typed in the column name. My problem is how can I use the variable
x
instead of typing the column name in this formula.
This is what I tried without success (they all return errors)

> df = data.frame(df %>% group_by(myGroup) %>% mutate(myRank = order(x,myEntity)))
> df = data.frame(df %>% group_by(myGroup) %>% mutate(myRank = order(as.name(x),myEntity)))
> df = data.frame(df %>% group_by(myGroup) %>% mutate(myRank = order(noquote(x),myEntity)))
> library(plyr)
> df = ddply(df,.(myGroup),transform,Order = rank(as.name(x)))


I also looked at the question here similar question but couldn't make it work for my scenario.

Answer Source

You could use the .data pronoun to refer to variables with strings:

x <- "myValue1"

df %>% 
  group_by(myGroup) %>% 
  mutate(myRank = order(.data[[x]], myEntity))
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