遍历数据帧并根据条件[R]更改值 [英] Iterating through data frame and changing values on condition [R]

问题描述

必须要记帐，因为这个for循环序列已经困扰了我很长时间了.

Had to make an account because this sequence of for loops has been annoying me for quite some time.

我在R中有一个数据帧，具有1000行和10列，每个值的范围为1:3.我想重新编码每个条目，以便:1 == 3，2 == 2，3 == 1.我知道，有更简便的方法可以做到这一点，例如对每个列进行子设置并对条件进行硬编码，但这并不总是理想的，因为我使用的许多数据集最多有100列.

I have a data frame in R with 1000 rows and 10 columns, with each value ranging from 1:3. I would like to re-code EVERY entry so that: 1==3, 2==2, 3==1. I understand that there are easier ways to do this, such as sub-setting each column and hard coding the condition, but this isn't always ideal as many of the data sets that I work with have up to 100 columns.

我想使用嵌套循环来完成此任务-到目前为止，这是我的目的:

I would like to use a nested loop in order to accomplish this task -- this is what I have thus far:

for(i in 1:nrow(dat_trans)){
  for(j in length(dat_trans)){
    if(dat_trans[i,j] == 1){
      dat_trans[i,j] <- 3
    } else if(dat_trans[i,j] == 2){
      dat_trans[i,j] <- 2
    } else{
      dat_trans[i,j] <- 1
    }
  }
}

所以我遍历第一列，获取每个值并根据if/else的条件对其进行更改，我仍在学习R，因此，如果我的代码中有任何指针，请随时指出.

So I iterate through the first column, grab every value and change it based on the if/else's condition, I am still learning R so if you have any pointers in my code, feel free to point it out.

代码

推荐答案

R是向量化语言，因此您实际上不需要内部循环.
另外，如果您注意到4-旧值" =新值"，则可以消除if语句.

R is a vectorized language, so you really don't need the inner loop.
Also if you notice that 4-"old value" = "new value", you can eliminate the if statements.

for(i in 1:ncol(dat_trans)){
        dat_trans[,i] <- 4-dat_trans[,i]
}

外部循环现在仅跨列迭代10次，而不是所有行1000次.这将大大提高性能.

The outer loop is now iterating across the columns for only 10 iterations as opposed to 1000 for all of rows. This will greatly improve performance.

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