Question

获得不等式表达式（字符）的下限和上限的正确方法是什么。这是一个例子：

df = structure(list(expressions = c("x<1", "x>1", "x==1", "x<=1", 
"x>=1")), .Names = "expressions", class = "data.frame", row.names = c(NA, 
-5L))

我的输入是df$expressions。我想获得df$minimum和df$maximum，如下所示

  expressions minimum maximum
1         x<1      NA 0.99999
2         x>1 1.00001      NA
3        x==1 1.00000 1.00000
4        x<=1      NA 1.00000
5        x>=1 1.00000      NA

当只有<时，从数字中减去1e-5。如果只有>，请在号码中添加1e-5。

Answer 1

可能不符合您要求的完整不同方法。但我想如果最终的目标是在实际数据上使用范围，你实际上也可以选择这种方法。

如果没有，值得尝试：

library(dplyr)

expressions = c('x < 1','x > 1','x == 1','x <= 1','x >= 1')

df <- data.frame(x = seq(0,2,by=1e-05))

df %>% mutate_(.dots=setNames(expressions, seq_along(expressions))) %>%
  gather(key,value, -x) %>% mutate(u = ifelse(value,x,NA)) %>%
  group_by(key) %>% summarise(minimum = min(u, na.rm=T), maximum = max(u, na.rm=T)) %>%
  mutate(key = factor(key, labels=expressions))

结果：

# A tibble: 5 × 3
     key minimum maximum
  <fctr>   <dbl>   <dbl>
1  x < 1 0.00000 0.99999
2  x > 1 1.00001 2.00000
3 x == 1 1.00000 1.00000
4 x <= 1 0.00000 1.00000
5 x >= 1 1.00000 2.00000

Answer 2

#FUNCTION
foo = function(eq, delta = 1e-5){
    #Extract the numerical portion of the expression
    n = as.numeric(gsub("\\D+", "", eq))

    #Create vector x
    x = c(-Inf, n - delta, n, n + delta, Inf)

    #Evaluate eq by plugging in x and subset values of x where TRUE
    y = x[eval(expr = parse(text = eq))]

    return(range(y))
}

t(sapply(df$expressions, foo))
#        [,1]    [,2]
#x<1     -Inf 0.99999
#x>1  1.00001     Inf
#x==1 1.00000 1.00000
#x<=1    -Inf 1.00000
#x>=1 1.00000     Inf

将不等式表达式（字符）解析为数值范围

2 个答案: