A question about looping and creating/joining tables - r

Question

My code is meant to order a table called Football (imported csv2) and then, using a for loop, go through the data and return the row number of the start year and end year.
Football[order(Football$Year),]
start_year <- min(Football$Year)
end_year <- max(Football$Year)
for (i in 1:nrow(Football)
{
if (Football$Year[i] = start_year)
{
row_of_start <- i
}
if (Football$Year[i] = end_year)
{
row_of_end <- i
}
}
This produces the following error:
> if (Football$Year[1] = start_year) row_of_start <- 1
Error: unexpected '=' in "if (Football$Year[1] ="
I appreciate there are probably ways of doing this without a for loop (which I would be very appreciative to know) although I would also like to know how to make the for loop work (to further my understanding).

Answer 1

You can skip the loop entirely using which(). This will usually be faster and more legible:
# Create example data
set.seed(123)
Football <- data.frame(Year = sample(1990:2000, size = 10),
foo = sample(letters, size = 10))
# Sort the data as you have done
Football_sort <- Football[order(Football$Year), ]
# Get the row numbers of the min and max (start and end years)
which(with(Football_sort, Year == min(Year)))
#> [1] 1
which(with(Football_sort, Year == max(Year)))
#> [1] 10
Depending upon what you actually want to do, you can skip the ordering step as well. Both of the below depend upon the dplyr package to work.
If you just want the start and end year rows rather than their row numbers:
library(dplyr)
Football %>%
filter(Year %in% c(min(Year), max(Year)))
#> Year foo
#> 1 2000 e
#> 2 1990 d
If you want the "year number" of the start and end year:
Football %>%
summarise(start_year = 1,
end_year = max(Year) - min(Year))
#> start_year end_year
#> 1 1 10