Working with Array in Stata

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Working with Array in Stata

• Vivien W. Chen
• Izumi Mori

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Do you

• Write repetitive programs for a set of variables
  or data files?
• Use longitudinal data that repeat the same data
  management for multiple years?
• Want to reduce the chance of coding errors due to
  repeated programming?

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The Purpose of This Workshop

• Introduce the corresponding programs to SAS array
  in Stata forvalue foreach
• Include the use of macro local global
• Introduce programs for temporary files and
  variables tempvar tempvar
• Reshape data structure for longitudinal data

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Example Data
Variable name Variable label Value label
country Country code ISO 3-digit
cnt Country code 3-character
female female 1female, 0male
fborn Foreign-born student 1foreign-born, 0native-born
Hisei (occ) Highest parental occupational status (SEI) continuous
Misced (med) Educational level of mother (ISCED) 0lowest to 6highest
cultposs Cultural possessions at home PISA 2006 (WLE) continuous
pv1math Plausible value in math continuous
(Source data PISA 2000, 2003, 2006)
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The Use of forvalues foreach

• forvalues is a loop that executes commends with a
  defined numeric local macro. Specific numbers or
  a range of numbers can be added in the macro
  before braces and . A range may be 1/5,
  meaning 1 to 5 or 0(5)100, indicating 0 to 100
  in steps of 5.

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• Example 1 replace missing values for XXX in each
  year file
• One solution is
• use file2000,clear
• replace XXX. If XXXlt0
• use file2003,clear
• replace XXX. If XXXlt0
• use file2006,clear
• eplace XXX. If XXXlt0
• Alternatively
• forv n2000 2003 2006
• use filen,clear
• replace XXX. If XXXlt0

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• foreach is a more generally useful statement. It
  can work with a list of variables, numbers, and
  names. It also can create new variable list.
• Example 2 (the same task as example 1)
• foreach n of numlist 2000 2003 2006
• use filen,clear
• replace XXX. If XXXlt0

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• Example 3 In each year file, (1) create dummy
  variables for mothers education (2)create
  interactions terms for gender, foreign born with
  mother edu and parental occ (3) create a year ID
  in each file and (4) append those files
  together.
• foreach n of numlist 2000 2003 2006
• use filen,clear
• tab med, gen(med)
• foreach x of varlist female fborn
  
• gen x_occxocc
• foreach n2 of numlist 0/6
• gen x_medn2xmedn2
• gen yrn
• use file2000,clear
• append using file2003 file 2006

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3
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• Are these the alternatives?
• foreach n of numlist 2000 2003 2006
• use filen,clear
• tab med, gen(med)
• foreach x of varlist female fborn
  
• gen x_occxocc
• gen x_medxmed (?)
• gen yrn
• append using filen (?)

If you want to interact with the continuous
variable of mothers education, you can do so.
This wont work, because its in the loop of each
year.
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Make Use of Macro local global

• A local macro is created in a do file and ceases
  while the do file terminates.
• A global macro terminates while a user exits
  Stata program

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• Example 4 regression analysis
• local x1 female fborn
• local x2 occ med1-med6 cultposs
• / global x1 female fborn
• global x2 occ med1-med6 cultposs /
• reg p1vmath x1
• reg p1vmath x1 x2
• / reg p1vmath x1
• reg p1vmath x1 x2 /
• Can I just use by instead of foreach country?