Translating loop syntax from Stata to R - r

Question

I need to write a for loop to calculate the product of year variables (e.g. var1874) * price variables (e.g. num1874), creating a new variable for each year and its corresponding price value (e.g. newvar1874).
Here's my data in R
A tibble: 4 x 7
cty var1874 var1875 var1876 num1874 num1875 num1876
<dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
1 1 0.78 0.83 0.99 2.64 2.8 3.1
2 2 0.69 0.69 0.89 2.3 2.3 2.58
3 3 0.42 0.48 0.59 2.28 2.44 2.64
4 4 0.82 0.94 1.09 2.28 2.36 3
I've been able to do this using the 'foreach' loop in Stata:
local vn 1874 1875 1876
foreach v of local vn {
gen newvar'v' = var'v'*num'v'
Does anyone know how I would do this same type of command using the for loop in R? I know there may be simpler ways to do this without the for loop, but I need to know how to do this using the for loop.

Answer 1

Using a for loop you could do:
vn <- 1874:1876
for (v in vn) d[[paste0("newvar", v)]] <- d[[paste0("var", v)]] * d[[paste0("num", v)]]
d
#> cty var1874 var1875 var1876 num1874 num1875 num1876 newvar1874 newvar1875
#> 1 1 0.78 0.83 0.99 2.64 2.80 3.10 2.0592 2.3240
#> 2 2 0.69 0.69 0.89 2.30 2.30 2.58 1.5870 1.5870
#> 3 3 0.42 0.48 0.59 2.28 2.44 2.64 0.9576 1.1712
#> 4 4 0.82 0.94 1.09 2.28 2.36 3.00 1.8696 2.2184
#> newvar1876
#> 1 3.0690
#> 2 2.2962
#> 3 1.5576
#> 4 3.2700
Or using lapply you could do:
d[, paste0("newvar", vn)] <- lapply(vn, function(v) d[[paste0("var", v)]] * d[[paste0("num", v)]])
DATA
d <- structure(list(
cty = 1:4, var1874 = c(0.78, 0.69, 0.42, 0.82),
var1875 = c(0.83, 0.69, 0.48, 0.94), var1876 = c(
0.99, 0.89,
0.59, 1.09
), num1874 = c(2.64, 2.3, 2.28, 2.28), num1875 = c(
2.8,
2.3, 2.44, 2.36
), num1876 = c(3.1, 2.58, 2.64, 3)
), class = "data.frame", row.names = c(
"1",
"2", "3", "4"
))