You probably heard that you shouldn’t use loops in R a thousand times by now, but there are some times you can’t avoid it. I recently had to implement a loop to generate a new variable in a dataset; the problem, how do I create the new variable and then put it back in a data.frame? Use assign
code example:
# create an empty dataset
df <- data.frame(obs = 1:10)
# create a list of values (strings) to iterate through
clist <- list("a", "b", "c")
# here comes the loop
for (i in clist) {
# in each loop assign the values to a variable matching
# the string corresponding to the actual iteration
assign(i, rnorm(10))
# use mget to put the vector back in the dataframe
df <- data.frame(df, mget(i))
}
There must be a million ways of doing this in a more efficient way, but this works great for a smallish dataset.
The result:
df
obs a b c
1 1 -0.6043081 -0.55737494 0.55271123
2 2 1.7190841 0.76963270 -1.20019177
3 3 -0.6397346 -1.01280031 -0.88938821
4 4 1.2044493 0.53935314 0.98288657
5 5 1.5952527 1.37572210 0.18416401
6 6 1.6863256 1.57793910 0.52359373
7 7 0.4624379 1.97033926 0.09766545
8 8 -0.3982681 -2.72841091 -0.91980220
9 9 1.3184167 -1.48644095 -0.07343118
10 10 1.2830817 0.05275999 1.92037378
Have a great weekend!
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