我有一个这样的数据框：

antecedents   consequents   lift
hamburger     pizza         1.1
pizza         hamburger     1.1
pasta         pizza         1.3
pizza         pasta         1.3 
apples        oranges       2.5
oranges       apples        2.5
apples        hamburger     .7
hamburger      apples       .7
oranges        hamburger    .5
hamburger      oranges      .5
pasta          apples       .6
apples         pasta        .6
pizza          apples       .3 
apples         pizza        .3
oranges        pizza        .2
pizza          oranges      .2

当我拥有上述数据框时，如何创建上三角矩阵？