Automate Creation of Change Variables in Wide Dataset in R

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I have a wide dataset with ~300 columns for ~150 biomarkers - each biomarker has a baseline value and a final value. I need to create a change variable (final - baseline) for each biomarker. I have been doing this manually when I have 10 variables, but I'm hoping for a more automated solution. This is what I'm currently doing:

df$marker1_chg = df$marker1_final - df$marker1_bl
df$marker2_chg = df$marker2_final - df$marker2_bl

And here is an example dataset:

data <- data.frame(c(1, 2, 3, 4, 5),
                   c(2, 2.3, 3.4, 3.6, 4.1),
                   c(3.1, 4.3, 4.4, 2.3, 4.6),
                   c(2.2, 5.4, 6.9, 3.9, 2.1),
                   c(3.5, 4.1, 6.7, 5.4, 3.8))
colnames(data) <- c('id', 'marker1_bl', 'marker1_final', 'marker2_bl', 'marker2_final')
r
2 Answers

Try this

lst <- list()
for(i in 1:150){
    lst[[i]] <- data[[paste0("marker" , i , "_final")]] - data[[paste0("marker" , i , "_bl")]]
}

names(lst) <- paste0("marker" , 1:150 , "_ch")

ans <- data.frame(lst)
user_191983370

Another possible solution:

library(tidyverse)

map2_dfc(select(data, ends_with("_final")) %>% relocate(order(names(.))), 
         select(data, ends_with("_bl")) %>% relocate(order(names(.))), 
         ~ .x - .y) %>% 
  set_names(str_replace(names(.), "final", "chg")) %>% 
  bind_cols(data, .)

#>   id marker1_bl marker1_final marker2_bl marker2_final marker1_chg marker2_chg
#> 1  1        2.0           3.1        2.2           3.5         1.1         1.3
#> 2  2        2.3           4.3        5.4           4.1         2.0        -1.3
#> 3  3        3.4           4.4        6.9           6.7         1.0        -0.2
#> 4  4        3.6           2.3        3.9           5.4        -1.3         1.5
#> 5  5        4.1           4.6        2.1           3.8         0.5         1.7
user_115644870
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