Calculating age over multiple dataframes based on name of dataframe - r

Question

I was wondering if someone here can help me with a lapply question.
Every month, data are extracted and the data frames are named according to the date extracted (01-08-2019,01-09-2019,01-10-2019 etc). The contents of each data frame are similar to the example below:
01-09-2019
ID DOB
3 01-07-2019
5 01-06-2019
7 01-05-2019
8 01-09-2019
01-10-2019
ID DOB
2 01-10-2019
5 01-06-2019
8 01-09-2019
9 01-02-2019
As the months roll on, there are more data sets being downloaded.
I am wanting to calculate the ages of people in each of the data sets based on the date the data was extracted - so in essence, the age would be the date difference between the data frame name and the DOB variable.
01-09-2019
ID DOB AGE(months)
3 01-07-2019 2
5 01-06-2019 3
7 01-05-2019 4
8 01-09-2019 0
01-10-2019
ID DOB AGE(months)
2 01-10-2019 0
5 01-06-2019 4
8 01-09-2019 1
9 01-02-2019 8
I was thinking of putting all of the data frames together in a list (as there are a lot) and then using lapply to calculate age across all data frames. How do I go about calculating the difference between a data frame name and a column?

Answer 1

If I may suggest a slightly differen approach: It might make more sense to compress your list into a single data frame before calculating the ages. Given your data looks something like this, i.e. it is a list of data frames, where the list element names are the dates of access:
$`01-09-2019`
# A tibble: 4 x 2
ID DOB
<dbl> <date>
1 3 2019-07-01
2 5 2019-06-01
3 7 2019-05-01
4 8 2019-09-01
$`01-10-2019`
# A tibble: 4 x 2
ID DOB
<dbl> <date>
1 2 2019-10-01
2 5 2019-06-01
3 8 2019-09-01
4 9 2019-02-01
You can call bind_rows first with parameter .id = "date_extracted" to turn your list into a data frame, and then calculate age in months.
library(tidyverse)
library(lubridate)
tib <- bind_rows(tib_list, .id = "date_extracted") %>%
mutate(date_extracted = dmy(date_extracted),
DOB = dmy(DOB),
age_months = month(date_extracted) - month(DOB)
)
#### OUTPUT ####
# A tibble: 8 x 4
date_extracted ID DOB age_months
<date> <dbl> <date> <dbl>
1 2019-09-01 3 2019-07-01 2
2 2019-09-01 5 2019-06-01 3
3 2019-09-01 7 2019-05-01 4
4 2019-09-01 8 2019-09-01 0
5 2019-10-01 2 2019-10-01 0
6 2019-10-01 5 2019-06-01 4
7 2019-10-01 8 2019-09-01 1
8 2019-10-01 9 2019-02-01 8

Answer 2

This can be solved with lapply as well but we can also use Map in this case to iterate over list and their names after adding all the dataframes in a list. In base R,
Map(function(x, y) {
x$DOB <- as.Date(x$DOB)
transform(x, age = as.integer(format(as.Date(y), "%m")) -
as.integer(format(x$DOB, "%m")))
}, list_df, names(list_df))
#$`01-09-2019`
# ID DOB age
#1 3 0001-07-20 2
#2 5 0001-06-20 3
#3 7 0001-05-20 4
#4 8 0001-09-20 0
#$`01-10-2019`
# ID DOB age
#1 2 0001-10-20 0
#2 5 0001-06-20 4
#3 8 0001-09-20 1
#4 9 0001-02-20 8
We can also do the same in tidyverse
library(dplyr)
library(lubridate)
purrr::imap(list_df, ~.x %>% mutate(age = month(.y) - month(DOB)))
data
list_df <- list(`01-09-2019` = structure(list(ID = c(3L, 5L, 7L, 8L),
DOB = structure(c(3L, 2L, 1L, 4L), .Label = c("01-05-2019", "01-06-2019",
"01-07-2019", "01-09-2019"), class = "factor")), class = "data.frame",
row.names = c(NA, -4L)), `01-10-2019` = structure(list(ID = c(2L, 5L, 8L, 9L),
DOB = structure(c(4L, 2L, 3L, 1L), .Label = c("01-02-2019",
"01-06-2019", "01-09-2019", "01-10-2019"), class = "factor")),
class = "data.frame", row.names = c(NA, -4L)))

Answer 3

It's bad practice to use dates and numbers as dataframe names consider prefix the date with an "x" as shown below in this base R solution:
df_list <- list(x01_09_2019 = `01-09-2019`, x01_10_2019 = `01-10-2019`)
df_list <- mapply(cbind, "report_date" = names(df_list), df_list, SIMPLIFY = F)
df_list <- lapply(df_list, function(x){
x$report_date <- as.Date(gsub("_", "-", gsub("x", "", x$report_date)), "%d-%m-%Y")
x$Age <- x$report_date - x$DOB
return(x)
}
)
Data:
`01-09-2019` <- structure(list(ID = c(3, 5, 7, 8),
DOB = structure(c(18078, 18048, 18017, 18140), class = "Date")),
class = "data.frame", row.names = c(NA, -4L))
`01-10-2019` <- structure(list(ID = c(2, 5, 8, 9),
DOB = structure(c(18170, 18048, 18140, 17928), class = "Date")),
class = "data.frame", row.names = c(NA, -4L))