Question

我无法弄清楚这段代码有什么问题。我有一个名为Fish的数据框。我想添加一个名为CombineMe的列，默认为0.如果满足两个条件，则值将更改为501（数据源= A＆amp; sample method = visual，那么它将等于501，如果数据源= B＆amp; taxon代码是三个EJ，EL或RV）。我无法弄清楚我哪里出错了。我已经尝试调整[i]的位置并添加逗号......

for(i in 1:length(Fish)) {
Fish$CombineMe <- 0 
if (Fish$data_source == "A" & Fish$sample_method == "visual") {
  Fish$CombineMe [i] <- 501
} else if (Fish$data_source == "B" & Fish$taxon_name == c("EJ", "EL", "RV")){
  Fish$CombineMe [i] <- 501
}}

这是鱼的样子的简明例子：

Fish <- data.frame ("data_source"=c("A", "A", "B", "C", "C", "D", "D"), "sample_method"= c("visualfish", "fish", "fish", "fish", "fish", "fish", "fish"), 
                  "taxon_name"=c("EJ", "EJ", "RV", "EJ", "RV", "EL", "HR"))

Answer 1

通常，您需要提供Fish数据帧的外观。我试着根据你给出的代码猜测：

Fish$CombineMe <- 0 
for(i in 1:nrow(Fish)) {

if (Fish$data_source[i] == "A" & Fish$sample_method[i] == "visual") {
  Fish$CombineMe[i] <- 501
} else if (Fish$data_source[i] == "B" & Fish$taxon_name[i] %in% c("EJ", "EL", "RV")){
  Fish$CombineMe [i] <- 501
}}

但我认为你不需要循环。以下是使用ifelse的替代方法。

Fish$CombineMe <- 0
Fish$CombineMe <- ifelse(Fish$data_source == "A" & Fish$sample_method == "visual", 501, Fish$CombineMe)
Fish$CombineMe <- ifelse(Fish$data_source == "B" & Fish$taxon_name %in% c("EJ", "EL", "RV"), 501, Fish$CombineMe)

Answer 2

这是令人讨厌的代码行：

Fish$CombineMe <- 0

对于循环的每次迭代，您将整个列归零。将它移到外面和循环之前它应该可以工作。

但是R是一种矢量化语言，更好的制作方法甚至根本不使用循环：

cond1 <- Fish$data_source == 'A' & Fish$sample_method == 'visual'
cond2 <- Fish$data_source == "B" & Fish$taxon_name %in% c('EJ', 'EL', 'RV')
Fish$CombineMe <- ifelse(cond1 | cond2, 501, 0)

Answer 3

您遇到的问题是因为每次循环时都定义Fish$CombineMe <- 0，因此您每次都要将孔列重新设置为cero。解决这个问题：

Fish$CombineMe[i] <- 0

for循环使用条件if语句

3 个答案: