Stata:变量的元素 [英] Stata: Elements of variable

问题描述

如何编辑变量的每第二个值?

How can I edit every 2nd value of a variable?

我的代码是:

set obs 100
gen u = invnorm(uniform())
forvalues d = 1/50 {
gen u[2*d] = u[2*d] + 1
}

我的代码有什么问题?

推荐答案

generate 的语法除了存储类型和变量名(以及标签名，这里无关紧要)之外不允许任何东西generate 和 = 之前.帮助文件中明确指出了这一点.

The syntax for generate doesn't allow anything except a storage type and variable name (and a label name, irrelevant here) after generate and before =. This is clearly indicated by the help file.

这里不需要循环.如果你想处理观察 2, 4, ... 那么

You don't need a loop here. If you want to work on observations 2, 4, ... then

 gen new_u = u + 1 if mod(_n, 2) == 0 

选择偶数观察数字.更改现有变量 generate 是非法的，但您可以使用

selects even observation numbers. To change an existing variable generate is illegal, but you could go

 replace u = u + 1 if mod(_n, 2) == 0 

 mod(_n, 2) == 0 

是

!mod(_n, 2) 

鉴于整数除以 2 的模数(严格来说，余数)只能是 1 或 0，所以否定零(逻辑假)给你一个(逻辑真).

given that the modulus (strictly, remainder) on dividing integers by 2 can only be 1 or 0, so negating zeros (logical false) gives you ones (logical true).

附言

invnorm(uniform())

是一种用均值 0 和方差 1 调用随机正态偏差的古老方法.在现代 Statas 中

is an ancient way to call random normal deviates with mean 0 and variance 1. In modern Statas

rnormal()

会做的.

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