Question

I am comparing a bunch of baseline and end-of-study differences across groups. For examples, I may have the following data set:

> baseline.comp
                             cluster 1970_pred 2008_pred  ratio   diff
 9  Many Transitions, Middle Income    0.1156    0.0248 4.6613 0.0908
10     Many Transitions, Low Income    0.1779    0.0389 4.5733 0.1390
 4       Dictatorships, High Income    0.1403    0.0307 4.5700 0.1096
 7    One Transition, Middle Income    0.0801    0.0219 3.6575 0.0582
 1         Democracies, High Income    0.0396    0.0116 3.4138 0.0280
 5     Dictatorships, Middle Income    0.1252    0.0399 3.1378 0.0853
 2       Democracies, Middle Income    0.0811    0.0291 2.7869 0.0520
 8       One Transition, Low Income    0.1912    0.0775 2.4671 0.1137
 3          Democracies, Low Income    0.1612    0.0698 2.3095 0.0914
 6        Dictatorships, Low Income    0.1854    0.0821 2.2582 0.1033

In this example, I would like to compare the column pred_1970 with itself so that I could have a table telling me about the differences in baseline conditions across these clusters. It would a 10 by 10 table but only the bellow diagonal cells would have actuall numbers, reflecting the differences in the initial conditions for these groups. I was wondering if R already has some implemented functionally to do that.

Thank you,

Antonio Pedro

Answer 1

outer is what you are looking for.

baseline_diff <- outer(baseline.comp[['1970_pred']],baseline.comp[['1970_pred']], '-')
## if you want to set the dimension names (but they will be very long!)
# dimnames(baseline_diff) <- list(baseline.comp[['cluster']],
#                                  baseline.comp[['cluster']])
 baseline_diff
          [,1]    [,2]    [,3]    [,4]   [,5]    [,6]    [,7]    [,8]    [,9]   [,10]
 [1,]  0.0000 -0.0623 -0.0247  0.0355 0.0760 -0.0096  0.0345 -0.0756 -0.0456 -0.0698
 [2,]  0.0623  0.0000  0.0376  0.0978 0.1383  0.0527  0.0968 -0.0133  0.0167 -0.0075
 [3,]  0.0247 -0.0376  0.0000  0.0602 0.1007  0.0151  0.0592 -0.0509 -0.0209 -0.0451
 [4,] -0.0355 -0.0978 -0.0602  0.0000 0.0405 -0.0451 -0.0010 -0.1111 -0.0811 -0.1053
 [5,] -0.0760 -0.1383 -0.1007 -0.0405 0.0000 -0.0856 -0.0415 -0.1516 -0.1216 -0.1458
 [6,]  0.0096 -0.0527 -0.0151  0.0451 0.0856  0.0000  0.0441 -0.0660 -0.0360 -0.0602
 [7,] -0.0345 -0.0968 -0.0592  0.0010 0.0415 -0.0441  0.0000 -0.1101 -0.0801 -0.1043
 [8,]  0.0756  0.0133  0.0509  0.1111 0.1516  0.0660  0.1101  0.0000  0.0300  0.0058
 [9,]  0.0456 -0.0167  0.0209  0.0811 0.1216  0.0360  0.0801 -0.0300  0.0000 -0.0242
[10,]  0.0698  0.0075  0.0451  0.1053 0.1458  0.0602  0.1043 -0.0058  0.0242  0.0000

To display only the lower (or upper) triangle use tril or triu in the Matrix package

library(Matrix)

tril(baseline_diff)

10 x 10 Matrix of class "dtrMatrix"
      [,1]    [,2]    [,3]    [,4]    [,5]    [,6]    [,7]    [,8]    [,9]    [,10]  
 [1,]  0.0000       .       .       .       .       .       .       .       .       .
 [2,]  0.0623  0.0000       .       .       .       .       .       .       .       .
 [3,]  0.0247 -0.0376  0.0000       .       .       .       .       .       .       .
 [4,] -0.0355 -0.0978 -0.0602  0.0000       .       .       .       .       .       .
 [5,] -0.0760 -0.1383 -0.1007 -0.0405  0.0000       .       .       .       .       .
 [6,]  0.0096 -0.0527 -0.0151  0.0451  0.0856  0.0000       .       .       .       .
 [7,] -0.0345 -0.0968 -0.0592  0.0010  0.0415 -0.0441  0.0000       .       .       .
 [8,]  0.0756  0.0133  0.0509  0.1111  0.1516  0.0660  0.1101  0.0000       .       .
 [9,]  0.0456 -0.0167  0.0209  0.0811  0.1216  0.0360  0.0801 -0.0300  0.0000       .
[10,]  0.0698  0.0075  0.0451  0.1053  0.1458  0.0602  0.1043 -0.0058  0.0242  0.0000