r - 将循环结果附加到向量

Question

我正在尝试获取值“a”的计数大于或等于 2 的变量名称列表，并最终将其存储在向量 Morethan2 中，同样对 lessthan2 执行同样的操作。请帮助我实现这一目标。

df <- data.frame(a1 = c("a","a","b"),a2 = c("a","b","b"),a3 = c("a","a","a"))
for(x in names(df[1:3])){
  if(sum(df[x] =="a") >= 2){
    more2 = x
    } else{less2 = x}}
Lessthan2 = less2
Morethan2 = more2

预期结果:

Morethan2  : 'a1','a3'
Lessthan2  : 'a2'

Answer 1

我们可以使用 colSums获取 "a" 的计数在每一列中，然后对其进行子集化以获得 morethan2和 lessthan2 .

inds <- colSums(df == "a")
morethan2 <- names(inds)[inds >= 2]
lessthan2 <- names(inds)[inds < 2]

morethan2
#[1] "a1" "a3"
lessthan2
#[1] "a2"

如果我们想使用 for循环，我们可以做

i <- 1
j  <- 1
more2 <- numeric()
less2 <- numeric()

for(x in names(df)) {
   if(sum(df[[x]] =="a") >= 2) {
      more2[i] = x
     i= i + 1
   } else {
     less2[j] = x
     j = j + 1
   }
}