Macros

Stata supports a macro programming language.

Local Macros

Local macros are declared with the local command, and only exist in the local scope.

local stringvars var1 var2

destring `stringvars', force

To loop over words in a local macro, see here.

Note that looping creates local macros to store the current word. These local macros are accessed in the same manner

foreach v of local stringvars {
  destring `v', force
} 

Global Macros

Global macros are declared with the global command. Otherwise, the grammar and rules are exactly the same as local macros.

global COHORT 1

Generally these are discouraged, because their very nature (i.e. globally available) creates side-effects.

To loop over words in a global macro, see here.

Expressions

If a macro definition includes an equals sign (=), then what follows is evaluated as an expression.

. local count1 = _N
. local count2 _N
. display "`count1' vs. `count2'"
100 vs. _N
. display "`count1' vs. " `count2'
100 vs. 100

Functions

If a macro definition includes a colon (:), then what follows is a macro function.

local cohorttype: type cohort
if (strpos("`cohorttype'","str")>0) {
  destring cohort, replace
}

Note that the e(), r(), and s() functions expect an argument of scalars, macros, matrices, or functions.

Lists

The list macro function enables a domain-specific language based on sets.

local union: list a | b
local intersection: list a & b
local difference: list a - b    //To clarify: will *not* include exclusive elements of b

Note that in each of the above cases, order is preserved. Also note that every references list macro is assumed to be a local macro. To reference a global macro instead, specify it like global(a).

The list macro function also features sub-functions including:

local unique: list uniq nonunique
local duplciates: list dupes nonunique
local sorted: list sort unsorted
local length: list sizeof series

It is furthermore possible to test and compare lists.

local match: list a == b
local match: list a === b

In the first example, match will store 1 if the two lists are equivalent and are in the same order (and 0 otherwise). The second example is order agnostic.

local match: list needle in haystack
local match: list posof "needle" in haystack

In the first example, needle is a macro list and match will store 1 if all elements of needle are found in haystack. In the second example, "needle" is a value literal and match will store the character position where the value begins appearing in haystack.

See also

Stata manual for macros

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