Combining data horizontally refers to the process of
merging or joining multiple data sets into one data set. This process
is referred to as a horizontal combination because, in the final data
set, each observation (or horizontal row) will have variables from
more than one input data set.
It is useful to combine data horizontally if you have several data sets that contain different but related information. For example, suppose you have one data set that contains employee data with the variables IDNumber, Name, and Address, and another data set that contains employee data with the variables IDNumber and Salary. You can ...