Having trouble constructing a 2*2*2 contingency table-CodePudding

The file "Aspirin" contains a 2 × 2 × 2 contingency table with columns defined as follows.

Column 1: V1=Observation number. [Observations 1 to 8.]

Column 2: V2=Count. [Nonnegative integer count for each cell in the Table.]

Column 3: V3=Case/Control Factor. [Factor Level 1 (Controls) and Level 2 (Cases).]

Column 4: V4=Ulcer Type Factor. [Factor Level 1 (Gastric) and Level 2 (Duodenal).]

Column 5: V5=Aspirin Use Factor. [Factor Level 1 (Non-User) and Level 2 (User).]

> aspirin
  V1 V2 V3 V4 V5
1  1 62  1  1  1
2  2 39  2  1  1
3  3 53  1  2  1
4  4 49  2  2  1
5  5  6  1  1  2
6  6 25  2  1  2
7  7  8  1  2  2
8  8  8  2  2  2

I want to construct a 2x2x2 contingency table like the image above in R, so I typed the following code:

case_control=factor(aspirin$V3)
ulcer=factor(aspirin$V4)
use=factor(aspirin$V5)
table(case_control,ulcer,use)

But I get something like this:

, , use = 1

            ulcer
case_control 1 2
           1 1 1
           2 1 1

, , use = 2

            ulcer
case_control 1 2
           1 1 1
           2 1 1

I want a contingency table with counts, so obviously the result above is not what I'm desiring. Is there a way to fix this?

CodePudding user response：

In your case, just use

ftable(case_control,ulcer,use)

which returns a "flat" table

                   use 1 2
case_control ulcer        
1            1         1 1
             2         1 1
2            1         1 1
             2         1 1

The main problem here is, that you are discarding your count column. So as an alternative here is a - in my opinion - better approach: You could use xtabs together with ftable() (here used in a dplyr pipe):

library(dplyr)

df %>% 
  transmute(ID = V1,
            Count = V2,
            Case_Control = factor(V3,
                                  labels = c("Control", "Case")),
            Ulcer_Type = factor(V4,
                                labels = c("Gastric", "Duodenal")),
            Aspirin_Use = factor(V5,
                                 labels = c("Non-User", "User"))) %>% 
  xtabs(Count ~ Ulcer_Type   Case_Control   Aspirin_Use, data = .) %>% 
  ftable()

This returns

                        Aspirin_Use Non-User User
Ulcer_Type Case_Control                          
Gastric    Control                        62    6
           Case                           39   25
Duodenal   Control                        53    8
           Case                           49    8

Data

df <- structure(list(V1 = c(1, 2, 3, 4, 5, 6, 7, 8), V2 = c(62, 39, 
53, 49, 6, 25, 8, 8), V3 = c(1, 2, 1, 2, 1, 2, 1, 2), V4 = c(1, 
1, 2, 2, 1, 1, 2, 2), V5 = c(1, 1, 1, 1, 2, 2, 2, 2)), row.names = c(NA, 
-8L), class = c("tbl_df", "tbl", "data.frame"))