compute variable over the value of the difference between another variable this year and the previou-CodePudding

In the data below I want to compute the following ratio tr(year)/(op(year) - op(year-1). I would appreciate an answer with dplyr.

year     op    tr    cp
  <chr> <dbl> <dbl> <dbl>
1 1984     10  39.1  38.3
2 1985     55 132.   77.1
3 1986     79  69.3  78.7
4 1987     78  47.7  74.1
5 1988    109  77.0  86.4

this is the expected output


year2          ratio
1  1985   2.933333
2  1986   2.887500
3  1987 -47.700000
4  1988  -2.483871

I do not manage to get to any result...

CodePudding user response：

Use lag:

library(dplyr)
df %>% 
  mutate(year = year,
         ratio = tr / (op - lag(op)),
         .keep = "none") %>% 
  tidyr::drop_na()

#  year      ratio
#2 1985   2.933333
#3 1986   2.887500
#4 1987 -47.700000
#5 1988   2.483871

CodePudding user response：

We may use

library(dplyr)
 df1 %>% 
  reframe(year = year[-1], ratio =  tr[-1]/diff(op))

-output

year      ratio
1 1985   2.933333
2 1986   2.887500
3 1987 -47.700000
4 1988   2.483871

data

df1 <- structure(list(year = 1984:1988, op = c(10L, 55L, 79L, 78L, 109L
), tr = c(39.1, 132, 69.3, 47.7, 77), cp = c(38.3, 77.1, 78.7, 
74.1, 86.4)), class = "data.frame", row.names = c("1", "2", "3", 
"4", "5"))