Selecting rows and columns within .csv file automatically using r

Question

So I have created a database for my thesis and I want to compare substances in different situations to receive a P-value. In order to do this I have created a script in R which is sort of not automatically. I am very interested in how I can create a script which does this for my using a for loop. I want to select groups for every line but also every three columns.

Please let me know if this is possible. Thanks in advance!

Right now I am doing it like this. First select line 1 first three values and then select next three values on first line in order to compare them in the next step.

row1_1 <- my_data[1, 2:4]
row1_2 <- my_data[1, 6:8]

Answer 1

The following will use a for loop to go through every row, as per the question

for (i in 1:nrow(my_data))
{

case1<- my_data[i, 2:4]
case2<- my_data[i, 6:8]
compare_cases <- t.test(case1, case2, alternative = "two.sided", var.equal = FALSE) 
print(case1)
print(case2)
print(compare_cases)
}

Modified variation with error handling, based on the comments

pvalues <- c()
for (i in 1:nrow(my_data))
{

  case1<- my_data[i, 2:4]
  case2<- my_data[i, 6:8]
  pval <- NA
  test <- tryCatch({ t.test(case1, case2, alternative = "two.sided", var.equal = FALSE) }, 
                     warning = function(war) { NA },
                     error = function(err) { NA },
                     finally = { })
  print(paste0("Test for row i=",i))
  print(test)
  if (identical(test,NA)) pval <- NA
  else pval <- test$p.value

  pvalues <- c(pvalues,pval)
}

print("All my pvalues for all rows are:")
print(pvalues)