Thursday, February 3, 2011

Regular expressions, an example

Why regular expressions are your friend. This is written in Stata but applies to any language where regular expressions exist.


Original version
if length("`qx'")==3 { /*ex: 5q0*/
local a = substr("`qx'", 1, 1)
local b = substr("`qx'", 3, 1)
}
else if substr("`qx'", 2, 1) == "q" & length("`qx'")==4 { /*ex: 5q20*/
local a = substr("`qx'", 1, 1)
local b = substr("`qx'", 3, 2)
}
else if substr("`qx'", 3, 1) == "q" & length("`qx'")==4 { /*ex: 10q5*/
local a = substr("`qx'", 1, 2)
local b = substr("`qx'", 4, 1)
}
else if length("`qx'")==5 { /*ex: 10q20*/
local a = substr("`qx'", 1, 2)
local b = substr("`qx'", 4, 2)
}


Regular expression version
foreach q in `qx' {
local a = regexr("`q'","q.+","")
local b = regexr("`q'",".+q","")
}

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