Create a variable that identifies earliest diagnosis and dates from 3 separate variables in R

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I have a dataframe in R with multiple columns for different diagnoses and dates associated with each diagnosis.

df = data.frame(ID = c(1001, 1002, 1003, 1004, 1005),
                Disease_code_1 = c('I802', 'G200','I802',NA, 'H356'),
                Disease_code_2 = c('A071',NA,'G20',NA,'H250'),
                Disease_code_3 = c('H250', NA,NA,NA,NA),
                Date_of_diagnosis_1 = c('12/06/1997','13/06/1997','14/02/2003',NA,'18/20/2005'),
                Date_of_diagnosis_2 = c('12/06/1998',NA,'18/09/2001',NA,'12/07/1993'),
                Date_of_diagnosis_3 = c('17/09/2010',NA,NA,NA,NA))

    ID Disease_code_1 Disease_code_2 Disease_code_3 Date_of_diagnosis_1 Date_of_diagnosis_2 Date_of_diagnosis_3
1 1001           I802           A071           H250          12/06/1997          12/06/1998          17/09/2010
2 1002           G200           <NA>           <NA>          13/06/1997                <NA>                <NA>
3 1003           I802            G20           <NA>          14/02/2003          18/09/2001                <NA>
4 1004           <NA>           <NA>           <NA>                <NA>                <NA>                <NA>
5 1005           H356           H250           <NA>          18/20/2005          12/07/1993                <NA>

But the dates and first diagnoses are not in order across the variables. I have created a variable to list the date of first diagnosis as it is necessary for my covariates, but also need to know which diagnosis was first. I have tried an ifelse function, but am not sure how to link these together to create a "firstdiagnosis" variable.

df$mindate <- apply(data[,c("Disease_code_1","Disease_code_2","Disease_code_3")],1,min, na.rm = TRUE)
r
1 Answers

First, you need to make sure your dates are recognized as dates. Then you can use pmin to find the minimum date across the row.

That being said there were dates that are invalid as a commenter pointed out. I fixed these to demonstrate this code.

library(lubridate)
library(tidyverse)

df1 <- mutate(df, 
              across(starts_with("Date"), dmy),      # format as dates
              first = pmin(Date_of_diagnosis_1, 
                                Date_of_diagnosis_2, # find the min date
                                Date_of_diagnosis_3,
                                na.rm = T))
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