You can use unnest from tidyr. See below:
x <- c(10, 15)
y <- c(20, 33)
z <- c(4, 8)
a <- data.frame(x, y, z)
names(a) <- c("F", "T", "L")
T1 <- function(a, b, c)
{
x1 <- seq(from = a,
to = b,
length = c)
}
a$Sam <- mapply(T1, a$F, a$T, a$L)
a
#> F T L
#> 1 10 20 4
#> 2 15 33 8
#> Sam
#> 1 10.00000, 13.33333, 16.66667, 20.00000
#> 2 15.00000, 17.57143, 20.14286, 22.71429, 25.28571, 27.85714, 30.42857, 33.00000
tidyr::unnest(a, Sam)
#> F T L Sam
#> 1 10 20 4 10.00000
#> 2 10 20 4 13.33333
#> 3 10 20 4 16.66667
#> 4 10 20 4 20.00000
#> 5 15 33 8 15.00000
#> 6 15 33 8 17.57143
#> 7 15 33 8 20.14286
#> 8 15 33 8 22.71429
#> 9 15 33 8 25.28571
#> 10 15 33 8 27.85714
#> 11 15 33 8 30.42857
#> 12 15 33 8 33.00000
Created on 2019-04-06 by the reprex package (v0.2.1)
Hope this helps.