Stack Variables

Convert from table form (rows corresponding to subjects) to long form (rows corresponding to observations).

In many cases, the data may be in tabular form, in which multiple observations are made but placed in different columns. An example of this may be a study of blood pressure on patients using several medications. The columns of this data set may be: patient.id, gender, drug, Week1, Week2, Week3. Here, each patient has their own row in the data set, but each row contains three observations of blood pressure.

patient.id	gender	drug	Week1	Week2	Week 3
1	male	A	130	125	120
2	male	B	140	130	110
3	female	A	120	119	116

We may want to convert to long form, where we have each observation in a new row, and use a categorical variable to differentiate the weeks. In this case, we would select Week1, Week2, and Week3 as the variables in the list. The new data set will have the columns patient.id, gender, drug, Stack.variable ("Week"), and stack.value ("blood pressure").

patient.id	gender	drug	stack.variable	stack.value
1	male	A	Week1	130
1	male	A	Week2	125
1	male	A	Week3	120
2	male	B	Week1	140
2	male	B	Week2	130
2	male	B	Week3	110
3	female	A	Week1	120
3	female	A	Week2	119
3	female	A	Week3	116

Of course, you can rename the variables as appropriate using Manipulate Variables > Rename Variables.