To find Maximum date

[kmmukesh]

Hi All,
I am new to R programming!
I am trying to find the maximum date, I've tried to use 'max' , but it showing error as 'NA'
I also have tried to convert into a date format, but was not successful. Any workaround?
Thanks

[siddharthprabhu]

It's hard for us to help without seeing your code. It would be ideal if you could provide a reproducible example (reprex). Please read this guide to see how to create one:

FAQ: How to do a minimal reproducible example ( reprex ) for beginners

A minimal reproducible example consists of the following items: A minimal dataset, necessary to reproduce the issue The minimal runnable code necessary to reproduce the issue, which can be run on the given dataset, and including the necessary information on the used packages. Let's quickly go over each one of these with examples: Minimal Dataset (Sample Data) You need to provide a data frame that is small enough to be (reasonably) pasted on a post, but big enough to reproduce your issue. Let's say, as an example, that you are working with the iris data frame head(iris) #> Sepal.Length Sepal.Width Petal.Length Petal.Width Species #> 1 5.1 3.5 1.4 0.…

[kmmukesh]

This is the sample code.

Subject_Visits$SVST_DT
[1] "2017-02-13 UTC" "2017-03-13 UTC" "2017-04-10 UTC"
[4] "2017-05-10 UTC" "2017-06-08 UTC" "2017-07-06 UTC"
[7] "2017-08-07 UTC" "2017-09-06 UTC" "2017-09-25 UTC"
max(Subject_Visits$SVST_DT)
[1] NA

You can see above the max date from the above data shows as "NA".

[phiggins]

From SO:

Min and Max of a date column in a dataframe

[kmmukesh]

Thanks! it helps! one question- if we want to find out max date for each subject as mentioned below:
SubjectA- Date1
SubjectA- Date2
SubjectB-Date1
SubjectB- Date2
Do you have any suggestion?

[phiggins]

First group_by(subject), then summarize(maxDate = max(date))

[kmmukesh]

It didn't seems to be working, it is taking the latest date of the column. any other suggestion?

[siddharthprabhu]

@kmmukesh That is not a reproducible example because we cannot recreate the Subject_Visits object from the code you have supplied. Please read the guide I linked to more carefully as that will increase your chances of getting help from the community.

Since I don't have a sample of your data, I'll make up some of my own to illustrate @phiggins' solution.

library(dplyr, warn.conflicts = FALSE)
library(lubridate, warn.conflicts = FALSE)

df <- tribble(~ subject, ~ date,
              "A", "2017-02-13 UTC",
              "A", "2017-03-13 UTC",
              "A", "2017-04-10 UTC",
              "A", "2017-05-10 UTC",
              "B", "2017-06-08 UTC",
              "B", "2017-07-06 UTC", 
              "B", "2017-08-07 UTC",
              "B", "2017-09-06 UTC",
              "B", "2017-09-25 UTC")

head(df)
#> # A tibble: 6 x 2
#>   subject date          
#>   <chr>   <chr>         
#> 1 A       2017-02-13 UTC
#> 2 A       2017-03-13 UTC
#> 3 A       2017-04-10 UTC
#> 4 A       2017-05-10 UTC
#> 5 B       2017-06-08 UTC
#> 6 B       2017-07-06 UTC

df %>% 
  mutate(date = ymd(date)) %>% # coerce column from character to date
  group_by(subject) %>% 
  summarize(max_date = max(date))
#> # A tibble: 2 x 2
#>   subject max_date  
#>   <chr>   <date>    
#> 1 A       2017-05-10
#> 2 B       2017-09-25

^{Created on 2020-03-25 by the reprex package (v0.3.0)}

[kmmukesh]

Thank you so much! will take care of posing sample data from the next post.