如何基于观察组的另一个变量为观察组创建一个新变量

Question

I'm trying add a new variable that is based on the observation for one level of a factor within a groups in my dataset. I've been trying to utilize various dplyr functions ( filter , select , mutate , group_by ) but can't figure out how to get them to work together and accomplish my goal.

here is a sample of my data:

  rep   rate       n  mort   avg
   <fct> <fct>  <int> <dbl> <dbl>
 1 1     0.747     10     7   0.7
 2 1     0.373     10     7   0.7
 3 1     0.187     10     6   0.6
 4 1     0.0933    10     0   0  
 5 1     0.00      10     1   0.1
 6 2     0.747     10     7   0.7
 7 2     0.373     10     5   0.5
 8 2     0.187     10     1   0.1
 9 2     0.0933    10     4   0.4
10 2     0.00      10     0   0  

What I'm hoping to accomplish is to create a new variable called cont that is derived from the avg variable when rate == "0.00" . This variable would be the same for each observation within the same rep group. The final product would be a table similar to the one below:

  rep   rate       n  mort   avg  cont
   <fct> <fct>  <int> <dbl> <dbl> <dbl>
 1 1     0.747     10     7   0.7  0.1
 2 1     0.373     10     7   0.7  0.1
 3 1     0.187     10     6   0.6  0.1
 4 1     0.0933    10     0   0    0.1
 5 1     0.00      10     1   0.1  0.1
 6 2     0.747     10     7   0.7  0
 7 2     0.373     10     5   0.5  0
 8 2     0.187     10     1   0.1  0
 9 2     0.0933    10     4   0.4  0
10 2     0.00      10     0   0    0

I've tried the following code: data %>% group_by(rep) %>% filter(rate =="0.00") %>% select(avg) which results in a dataframe with the data that I do want added as the new variable:

  rep     avg
  <fct> <dbl>
1 1       0.1
2 2       0  
3 3       0.1
4 4       0.3
5 5       0  
6 6       0  
7 7       0  
8 8       0  

My problem now is that I have no idea how to create the new variable for each observation within the rep group. I'm not sure how to use mutate properly in this situation. Thank you in advance for any help!

Answer 1

Assuming there would be only one occurrence of rate == "0.00" in each group, we can do

library(dplyr)
df %>%
   group_by(rep) %>%
   mutate(cont = avg[rate == "0.00"])

#   rep   rate       n  mort   avg  cont
#  <fct> <fct>  <int> <dbl> <dbl> <dbl>
# 1 1     0.747     10     7   0.7   0.1
# 2 1     0.373     10     7   0.7   0.1
# 3 1     0.187     10     6   0.6   0.1
# 4 1     0.0933    10     0   0     0.1
# 5 1     0.00      10     1   0.1   0.1
# 6 2     0.747     10     7   0.7   0  
# 7 2     0.373     10     5   0.5   0  
# 8 2     0.187     10     1   0.1   0  
# 9 2     0.0933    10     4   0.4   0  
#10 2     0.00      10     0   0     0  

If there are more than one occurrence, we can use which.max to select the first one

df %>% group_by(rep) %>% mutate(cont = avg[which.max(rate == "0.00")])

---

Using data.table , we can do

library(data.table)
setDT(df)[, cont := avg[rate == "0.00"], by = rep]

data

df <- structure(list(rep = structure(c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 
2L, 2L, 2L), .Label = c("1", "2"), class = "factor"), rate = structure(c(5L, 
4L, 3L, 2L, 1L, 5L, 4L, 3L, 2L, 1L), .Label = c("0.00", "0.0933", 
"0.187", "0.373", "0.747"), class = "factor"), n = c(10L, 10L, 
10L, 10L, 10L, 10L, 10L, 10L, 10L, 10L), mort = c(7, 7, 6, 0, 
1, 7, 5, 1, 4, 0), avg = c(0.7, 0.7, 0.6, 0, 0.1, 0.7, 0.5, 0.1, 
0.4, 0)), row.names = c("1", "2", "3", "4", "5", "6", "7", "8", 
"9", "10"), class = "data.frame")

Answer 2

We can use match

library(dplyr)
df  %>%
   group_by(rep) %>% 
   mutate(cont = avg[match("0.00", rate)])
# A tibble: 10 x 6
# Groups:   rep [2]
#   rep   rate       n  mort   avg  cont
#   <fct> <fct>  <int> <dbl> <dbl> <dbl>
# 1 1     0.747     10     7   0.7   0.1
# 2 1     0.373     10     7   0.7   0.1
# 3 1     0.187     10     6   0.6   0.1
# 4 1     0.0933    10     0   0     0.1
# 5 1     0.00      10     1   0.1   0.1
# 6 2     0.747     10     7   0.7   0  
# 7 2     0.373     10     5   0.5   0  
# 8 2     0.187     10     1   0.1   0  
# 9 2     0.0933    10     4   0.4   0  
#10 2     0.00      10     0   0     0  

---

Or with data.table

library(data.table)
setDT(df)[, cont := avg[match("0.00", rate)], rep]

Or using the join as @thelatemail suggested

setDT(df)[df[rate=="0.00"], on= .(rep), cont := i.avg]

Note; Both the methods would work even if there are duplicate values as match returns only the index of the first match.

data

df <- structure(list(rep = structure(c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 
2L, 2L, 2L), .Label = c("1", "2"), class = "factor"), rate = structure(c(5L, 
4L, 3L, 2L, 1L, 5L, 4L, 3L, 2L, 1L), .Label = c("0.00", "0.0933", 
"0.187", "0.373", "0.747"), class = "factor"), n = c(10L, 10L, 
10L, 10L, 10L, 10L, 10L, 10L, 10L, 10L), mort = c(7, 7, 6, 0, 
1, 7, 5, 1, 4, 0), avg = c(0.7, 0.7, 0.6, 0, 0.1, 0.7, 0.5, 0.1, 
0.4, 0)), row.names = c("1", "2", "3", "4", "5", "6", "7", "8", 
"9", "10"), class = "data.frame")