Deriving contingency table from a bigger contingency table in R

Question

I have a csv format contingency table made by python language , like this:

            case  control
disease_A    20    30 
disease_B    35    45
disease_C    42    52
disease_D    52    62

now i want to derive 2x2 contingency tables from this contingency table to calculate chi-square value using R

how can i derive a 2x2 table like the following from the contingency table above:

            case  control
disease_A    20    30 
disease_D    52    62

Thats probably a novice question but im new to R and i couldn't find the solution anywhere else

Answer 1

Here's an approach.

The data:

txt <-  "           case  control
disease_A    20    30 
disease_B    35    45
disease_C    42    52
disease_D    52    62"

Read the data:

dat <- read.table(textConnection(txt))
#           case control
# disease_A   20      30
# disease_B   35      45
# disease_C   42      52
# disease_D   52      62

Extract a subset of rows:

dat2 <- dat[rownames(dat) %in% c("disease_A", "disease_D"), ]
#           case control 
# disease_A   20      30
# disease_D   52      62