Stata中一些令人困扰的易错函数——sum()和total()_stata total函数

• 问题：Stata中有两个求和函数sum()和total()，但由于历史原因，二者在一些场景下可能会产生意料之外、甚至错误的结果，特此撰文。

直接上代码：

* 产生一个变量v1
clear all
input v1
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end

* 用`gen`产生求和变量
gen gs = sum(v1)
gen gt = total(v1) // 报错：unknown function total()

* 用`egen`产生求和变量
egen egs = sum(v1)
egen egt = total(v1)

* 结果：
v1	gs	egs	egt
1	1	12	12
2	3	12	12
2	5	12	12
3	8	12	12
4	12	12	12
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原因

• help sum()
  sum(x): the running sum of x, treating missing values as zero.For example, following the command generate y=sum(x), the jth observation on y contains the sum of the first through jth observations on x. See [D] egen for an alternative sum function, total(), that produces a constant equal to the overall sum.
• help total()
  找不到这个函数，只有一个total（“produces estimates of totals, along with standard errors”)（注意区别）。也就是说， total()必须在egen中使用，表示overall sum。
• 如上， 特别值得注意的是，在egen中，sum()和total()得到的结果相同，但在gen中则不同。

• 官方说明：help whatsnew8to9

The following egen functions have been renamed:

	old name    new name
	
	any()       anyvalue()
	eqany()     anymatch()
	neqany()    anycount()
	rfirst()    rowfirst()
	rlast()     rowlast()
	rmean()     rowmean()
	rmin()      rowmin()
	rmiss()     rowmiss()
	robs()      rownonmiss()
	rsd()       rowsd()
	rsum()      rowtotal()
	sum()       total()
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The new names are more consistent. Old names continue to work but are not documented.

• 更多例子：

clear
set obs 5
generate x = _n if _n != 3

* Create variable containing the running sum of x
generate runsum = sum(x)

* Create variable containing a constant equal to the overall sum of x
egen totalsum = total(x)

* List the results
list
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