= Stata Looping =

Stata offers several structures and commands for '''looping'''; select the one most appropriate for ''what'' is being looped over.

<<TableOfContents>>

----



== Literal List ==

To iterate over tokens in a literal list, try:

{{{
foreach localname in a b c {
  replace string = subinstr(string, "`a'", "-", .)
}
}}}

----



== Local Macro List ==

To iterate over tokens in a local macro, try:

{{{
levelsof GROUPVAR, local(groups_of_GROUPVAR)

foreach localname of local groups_of_GROUPVAR {
  generate group = `localname'
}
}}}

----



== Global Macro List ==

To iterate over tokens in a global macro, try:

{{{
global CLOSED_COHORTS="1 2 3"

foreach localname of global COHORTS {
  assert complete==1 if cohort==`localname'
}
}}}

----



== Variable List ==

To iterate over a list of variables, try:

{{{
foreach localname of varlist VAR1-VAR9 {
  assert `localname' != .
}
}}}

Note that `_all` can be substituted for `*` to mean 'all variables.

----



== New Variable List ==

To iterate over a list of new variables, try:

{{{
foreach localname of newlist VAR1-VAR9 {
  generate `localname' = .
}
}}}

----



== Number List ==

to iterate over a number list, try:

{{{
foreach localname of numlist 1/9 {
  count if VAR==`localname'
}
}}}

Note that the syntax for number lists includes:

 * `a b c` (a literal number list)
 * `a,b,c` (same as above)
 * `a/b` (a range of ''a'' to ''b'', which can be ascending or descending)
 * `a to b` (same as above)
 * `a(i)b` (a range of ''a'' to ''b'' increasing or decreasing in increments of ''i'', which can be positive or negative, integer or decimal)
 * `a[i]b` (same as above)
 * and any combination of the above

----



== ForValues ==

An alternate syntax for iterating over number values is:

{{{
forvalues localname = 1/9 {
  count if VAR==`localname'
}
}}}

The rules for `forvalues` number lists are:

 * `a/b` (a range of ''a'' to ''b'', which can be ascending or descending)
 * `a(i)b` (a range of ''a'' to ''b'' increasing or decreasing in increments of ''i'', which can be positive or negative, integer or decimal)
 * `a b to c` (a range of ''a'' to ''c'' increasing or decreasing in increments of ''b''-''a'')
 * `a b : c` (same as above)



----
CategoryRicottone