When use Diff or just subtraction

[Shin1]

How can I calculate a long difference in occupations from 1990 to 2021. Example:
df <- data.frame(Occ=c("petroleum engineer", "data scientist"," telemarketer" ,"welders"),
Occupation_1990=c(30, 7,50, 40),
Occupation_2021=c(40, 50, 10, 20))
for the difference of this occupations should I use diff, and how, or just - ?

[FJCC]

If you want to find the difference between the Occupation_2021 and Occupation_1990, use the regular subtraction operator -.

df <- data.frame(Occ=c("petroleum engineer", "data scientist"," telemarketer" ,"welders"),
                  Occupation_1990=c(30, 7,50, 40),
                  Occupation_2021=c(40, 50, 10, 20))
df
                 Occ Occupation_1990 Occupation_2021
1 petroleum engineer              30              40
2     data scientist               7              50
3       telemarketer              50              10
4            welders              40              20
df$Difference <- df$Occupation_2021 - df$Occupation_1990
df
                 Occ Occupation_1990 Occupation_2021 Difference
1 petroleum engineer              30              40         10
2     data scientist               7              50         43
3       telemarketer              50              10        -40
4            welders              40              20        -20

If you want to fince differences within a vector, use diff

Vals <- c(2,6,3,12)
diff(Vals)
[1]  4 -3  9

The values 4, -3, 9 come from calculating along the vector:6 - 2 = 4, 3 - 6 = -3, 12 - 3 = 9

[Shin1]

thank you for your answers