I am new to both programming and R. While some components of R I've found

easy to navigate (R seems to be the best software in terms of a

self-teaching program and I've enjoyed learning it), I've really been

struggling to understand how to code for-loops, even in tutorials. For

example, one I've seen within a tutorial is

∑25 =1 ^2

sum <- 0

for(i in 1:25)

sum <- sum + i^2

sum

but this example doesn't fit into using the assignment operator and then

creating loops from there, which I think I would better understand (if this

is possible to do). Other examples I have found also seem very complex.

I was hoping to share a scenario in which a for-loop would be incredibly

helpful for the analyses I am running so that I may better understand how to

write a loop going forward.

I have a huge data set ("studydata") composed of rows of categorical

variables and columns of continuous variables. The data can be organized

into those 3 categorical variables-- let's call them PatientGroup1

PatientGroup2 and ControlGroup. Then there are over 30 measured continuous

variables I need to run t.tests on (let's say three of the variables, for

example, are A, B, and C). so that it looks like this:

A B C ...D,E,F,etc.

PatientGroup1 4 6 8

PatientGroup2 5 7 9

ControlGroup 10 15 20

*repeats*

I've managed to go ahead and assign the values of each variable to the

respective categorical variable using the assignment operator so that I have

"PatientGroup1" "PatientGroup2" and "ControlGroup." I know how to run a

t.test by setting up the following code (though it may be amateur):

Variable_A_PatientGroup1=PatientGroup1$'A'

Variable_A_PatientGroup2=PatientGroup2$'A'

t.test(Variable_A_PatientGroup1, Variable_A_PatientGroup2)

However, if I wanted to create a loop, so that this same code runs for

variables B,C, etc. Is that feasible? Or is there another easier method to

implement? I appreciate any feedback and apologize in advance for my amateur

question.