Abstraction & automation

Use abstract definitions

Do everything as abstract as possible. Try to never ever “hard code” values in your code. The reason is quite simple: Eventually, your data will change: There will be some additional data cleaning, data updates, or other changes to your data. If you write definitions etc. based on your current data in your code (e.g., define a new variable based on the current mean), they will become wrong as soon as the data changes - without you even noticing it!

Instead, use

• return & ereturn objects and system variables

Example using the return list of the sum command to create a new variable


• macros & macro functions

Example of defining a global with the exchange rate to convert currencies

Use automated (export) tables & graphs whenever possible (see the chapter on advanced graphs and tables and on dynamic documents).

Minimize copy & paste

Definitions etc. should be done at one point only to prevent inconsistencies and errors. This makes it also easier to change the definitions later on.

• Most obvious example: Use loops for repetitive tasks:

Screenshot of a loop replacing values and adding a note to variables


• Use the same do-file for definitions which re-occur at different steps, e.g., creating an index at base- & endline

Screenshot of two do-files calling on the same do-file named "wealth_quintiles"


• For more complex repetitive tasks: Write programs (.ado-files)

Use automated error checks

Write error checks in your code to make sure everything works as intended, using for example:

• isid
  Checks if a variable/a combination of variables uniquely identifies the observations. Use the option "missok" for missing values.
• confirm
  Tool for many checks, e.g., whether a variable is numeric, whether a file exists etc.
• assert
  Tests an expression, e.g. whether the sum of two variables equals a third variable for all observations (make sure to exempt missings, if applicable).

Also, you can use "assert" option of the merge command to control the merge. Example:

Variable lists

Should you use variable lists (e.g., lifeexp* or price-length)? They can be useful if variables are consistently ordered/named.
BUT: They can also easily lead to errors if the order or the names change! Consider using macros or the ds command:

Please note that some commands allow incomplete varnames as input, e.g., “med” instead of “medage” (not to be confused with “med*”)
This can easily lead to mistakes → use set varabbrev off

Helpful chapters