Stata Logic

Stata supports the following logic structures for programming.

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Operators

Arithmetic operators include:

String operators include:

There is an operator taking one integer argument and one string argument:

Relational operators include:

Relational operators resolve to values of 0 or 1, so they can be mixed with arithmetic operations.

Relational operators cannot be chained, i.e. 1 < 2 < 3 is not valid syntax.

Logical operators include:

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Conditional Processing

Most commands support an if EXPR clause. Reference the command's specific syntax.

replace foo = bar if baz==1

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If

A command can be made to operate conditionally in the sense that the command itself may or may not be called.

if ${debug}==1 assert errors==0

if ${debug}==1 {
  assert errors==0
}

An if structure can be followed by an else structure.

if ${debug}==1 assert errors==0
else display "Not in debug mode"

if ${debug}==1 {
  assert errors==0
}
else {
  display "Not in debug mode"
}

An 'elif'-type structure is only acheived by opening a new if structure on the else structure.

if ${debug}==1 {
  assert errors==0
}
else if ${debug}==0 {
  display "Not in debug mode"
}
else {
  display "Debug in unknown state"
}

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By

The by command prefix causes a command to be repeated within groups.

A common usecase of the by structure is for identifying duplciate cases.

sort foo bar baz
by foo bar baz: generate byte duplicate = cond(_N==1, 0, _n)

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