[R] sort

[Rui Barradas]

Hello,

Here is a dplyr solution. arrange() sorts by name and desc(ddate) and 
top_n keeps the first 2 after grouping by ddate. Then it's a matter of 
being careful with diff() in the summarise instruction.


library(dplyr)

DF1 %>%
   mutate(ddate = as.Date(ddate)) %>%
   arrange(name, desc(ddate)) %>%
   group_by(name) %>%
   top_n(2) %>%
   summarise(diff = ifelse(n() > 1, diff(rev(ddate)), 0))
#Selecting by ddate
## A tibble: 3 x 2
#  name   diff
#  <chr> <dbl>
#1 A        76
#2 B       305
#3 c         0


Hope this helps,

Rui Barradas

Às 03:58 de 15/05/20, Val escreveu:
> HI All,
> I have a sample of data frame
> DF1<-read.table(text="name ddate
>    A  2019-10-28
>    A  2018-01-25
>    A  2020-01-12
>    A  2017-10-20
>    B  2020-11-20
>    B  2019-10-20
>    B  2017-05-20
>    B  2020-01-20
>    c  2009-10-01  ",header=TRUE)
> 
> 1. I want sort by name and ddate on decreasing order and the output
> should like as follow
>     A  2020-01-12
>     A  2019-01-12
>     A  2018-01-25
>     A  2017-10-20
>     B  2020-11-21
>    B  2020-11-01
>    B  2019-10-20
>    B  2017-05-20
>    c  2009-10-01
> 
> 2.  Take the top two rows by group( names) and the out put should like
>     A  2020-01-12
>     A  2019-01-12
>     B  2020-11-21
>     B  2020-11-01
>      c  2009-10-01
> 
> 3.  Within each group (name) get the date difference  between the
> first and second rows dates. If a group has only one row then the
> difference should be 0
> 
> The final out put is
> Name diff
>     A  365
>      B  20
>      C  0
> 
> Here is my attempt and have an issue at the sorting
> DF1$DTime <- as.POSIXct(DF1$ddate , format = "%Y-%m-%d")
> DF2 <- DF1[order(DF1$name, ((as.Date(DF1$DTime, decreasing = TRUE)))), ]
> 
> not working
> Any help?
> 
> Thank you
> 
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