在 R 中仅按递增、升序过滤组

Question

我无法弄清楚如何过滤 dataframe 中按降序增加的组。 我将从一个输入开始：

df <- structure(list(Animal = c("Cat", "Cat", "Cat", "Cat", "Cat", 
"Cat", "Dog", "Dog", "Dog", "Dog", "Rat", "Rat", "Rat", "Rat", 
"Rat"), Value = c(2L, 3L, 5L, 8L, 19L, 20L, 4L, 8L, 19L, 33L, 
4L, 8L, 15L, 10L, 25L)), class = "data.frame", row.names = c(NA, 
-15L))

在这种情况下，我希望我的 output 只显示组“狗”和“猫”，因为它一直在增加。 然而，当它从 8 到 15 再到 10 时，老鼠会被排除在外。

任何帮助，将不胜感激。 谢谢！

Answer 1

一种基于dplyr的解决方案可能是：

df %>%
 group_by(Animal) %>%
 filter(all(diff(Value) > 0))

   Animal Value
   <chr>  <int>
 1 Cat        2
 2 Cat        3
 3 Cat        5
 4 Cat        8
 5 Cat       19
 6 Cat       20
 7 Dog        4
 8 Dog        8
 9 Dog       19
10 Dog       33

Answer 2

数据：

df <- structure(list(Animal = c("Cat", "Cat", "Cat", "Cat", "Cat", 
"Cat", "Dog", "Dog", "Dog", "Dog", "Rat", "Rat", "Rat", "Rat", 
"Rat"), Value = c(2L, 3L, 5L, 8L, 19L, 20L, 4L, 8L, 19L, 33L, 
4L, 8L, 15L, 10L, 25L)), class = "data.frame", row.names = c(NA, 
-15L))

代码：

library(dplyr)

df %>% 
  filter(!Animal == "Rat") %>% 
  arrange(Animal, Value)

Output：

#>    Animal Value
#> 1     Cat     2
#> 2     Cat     3
#> 3     Cat     5
#> 4     Cat     8
#> 5     Cat    19
#> 6     Cat    20
#> 7     Dog     4
#> 8     Dog     8
#> 9     Dog    19
#> 10    Dog    33

^{由reprex package (v0.3.0) 创建于 2020-08-18}

Answer 3

我会定义一个 function 称为increasing based on diff ，它返回 boolean。以下是dplyr和data.table的版本：

library(dplyr)
library(data.table)

df <- tibble::tribble(
~Animal,  ~Value,
"Cat", 2,
"Cat", 3,
"Cat", 5,
"Cat", 8,
"Cat", 19,
"Cat", 20,
"Dog", 4,
"Dog", 8,
"Dog", 19,
"Dog", 33,
"Rat", 4,
"Rat", 8,
"Rat", 15,
"Rat", 10,
"Rat", 25)
dt <- data.table(df)

increasing <- function(x) rep(all(diff(x) >= 0), length(x))

df %>% group_by(Animal) %>%
       filter(increasing(Value)) 

dt[, .SD[increasing(Value)], by=Animal]