I am relatively new to R and have data in wide format as follows
subject_id age sex treat1.1.param1 treat1.1.param2 treat1.2.param1 treat1.2.param2
-----------------------------------------------------------------------------------------------
1 23 M 1 2 3 4
2 25 W 5 6 7 8
which is data on several subjects for which we have for a given treatment (here treat1) measures several parameters (here param1 and param2) over multiple rounds of repeated measurements (here round 1 and round 2). The information which treatment, round and parameter the entry for this subject belongs to is coded in the column header as exemplified above.
I would like to have the data in long format exemplified as follows:
subject_id age sex treatment round param1 param2
------------------------------------------------------------------------------------------
1 23 M treat1 1 1 2
1 23 M treat1 2 3 4
2 25 W treat1 1 5 6
2 25 W treat1 2 7 8
That is, the id variable to identify a single observation are subject_id, treatment, round. But since the latter two variables are encoded in the column headers using dots as separators, I don't know how to move from the wide to long format as above. All tries with standard examples (using reshape2 or tidyr) have failed. Since in reality, I have 12 treatments with each 30 rounds and about 50 parameters per round, a relatively manual way of doing it would not help me too much.
We can use pivot_longer from tidyr specifying the names_to and names_pattern argument.
tidyr::pivot_longer(df,
cols = starts_with("treat"),
names_to = c("treatmeant", "round", ".value"),
names_pattern = "(\\w+)\\.(\\d+)\\.(\\w+)")
# subject_id age sex treatmeant round param1 param2
# <int> <int> <fct> <chr> <chr> <int> <int>
#1 1 23 M treat1 1 1 2
#2 1 23 M treat1 2 3 4
#3 2 25 W treat1 1 5 6
#4 2 25 W treat1 2 7 8
data
df <- structure(list(subject_id = 1:2, age = c(23L, 25L), sex = structure(1:2,
.Label = c("M", "W"), class = "factor"),
treat1.1.param1 = c(1L, 5L), treat1.1.param2 = c(2L, 6L),
treat1.2.param1 = c(3L, 7L), treat1.2.param2 = c(4L, 8L)),
class = "data.frame", row.names = c(NA, -2L))