r - 为什么给出0时没有+号？

Question

我正在尝试计算水平曲线列表，如下所示:

a = 0:10
colnames(c) = c("x1","w",paste0("x2+3x1",ifelse(3*a+1<0,"","+"),a+1,"=0"))

colnames(c)
 [1] "x1"          "w"           "x2+3x1-9=0"  "x2+3x1-8=0"  "x2+3x1-7=0" 
 [6] "x2+3x1-6=0"  "x2+3x1-5=0"  "x2+3x1-4=0"  "x2+3x1-3=0"  "x2+3x1-2=0" 
[11] "x2+3x1-1=0"  "x2+3x10=0"   "x2+3x1+1=0"  "x2+3x1+2=0"  "x2+3x1+3=0" 
[16] "x2+3x1+4=0"  "x2+3x1+5=0"  "x2+3x1+6=0"  "x2+3x1+7=0"  "x2+3x1+8=0" 
[21] "x2+3x1+9=0"  "x2+3x1+10=0" "x2+3x1+11=0"

但是，不要打印 "x2+3x1+0=0"对于第 12 个元素，它打印 "x2+3x10=0"尽管期待3*a+1<0返回FALSE当a==0 .

Answer 1

我创建了一个 data.frame，以便您可以检查 a = -1 的条件是否为 < 0。由于 -1 + 1 = 0，因此对于 a = -1 给出 x2+3x10=0。

因此，您可以将代码条件更改为 < -2，就像我在 result2 中所做的那样。

a <-  -5:5

library(dplyr)

data.frame(a) %>% 
  mutate(
    condition = 3*a+1,
    result1= paste0("x2+3x1",ifelse(condition< 0,"","+"),a+1,"=0"),
    result2= paste0("x2+3x1",ifelse(condition< -2,"","+"),a+1,"=0")
  )

    a condition    result1    result2
1  -5       -14 x2+3x1-4=0 x2+3x1-4=0
2  -4       -11 x2+3x1-3=0 x2+3x1-3=0
3  -3        -8 x2+3x1-2=0 x2+3x1-2=0
4  -2        -5 x2+3x1-1=0 x2+3x1-1=0
5  -1        -2  x2+3x10=0 x2+3x1+0=0
6   0         1 x2+3x1+1=0 x2+3x1+1=0
7   1         4 x2+3x1+2=0 x2+3x1+2=0
8   2         7 x2+3x1+3=0 x2+3x1+3=0
9   3        10 x2+3x1+4=0 x2+3x1+4=0
10  4        13 x2+3x1+5=0 x2+3x1+5=0
11  5        16 x2+3x1+6=0 x2+3x1+6=0