Conditional filtering with data.table with multiple statements-CodePudding

I would like to know if there is an elegant and concise way to do conditional filtering with data.table.

My aim is the following: if condition 1 is met, filter based on condition 2.

For instance, in the case of the iris dataset, how can I drop the observations among Species=="setosa" where Sepal.Length<5.5, while keeping all observations with Sepal.Length<5.5 for other species?

I know how to do this in steps, but I wonder if there is a better way to do it in a single liner

# this is how I would do it in steps. 

data("iris")

# first only select observations in setosa I am interested in keeping 
iris1<- setDT(iris)[Sepal.Length>=5.5&Species=="setosa"] 

# second, drop all of setosa observations. 
iris2<- setDT(iris)[Species!="setosa"] 

# join data,
iris_final<-full_join(iris1,iris2)

head(iris_final)
   Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
1:          5.8         4.0          1.2         0.2     setosa
2:          5.7         4.4          1.5         0.4     setosa
3:          5.7         3.8          1.7         0.3     setosa
4:          5.5         4.2          1.4         0.2     setosa
5:          5.5         3.5          1.3         0.2     setosa # only keeping setosa with Sepal.Length>=5.5. Note that for other species, Sepal.Length can be <5.5
6:          7.0         3.2          4.7         1.4 versicolor

is there a more concise and elegant way of doing this?

CodePudding user response：

Is something like the following what you are looking for? It is not very clear what you want.

library(data.table)

dt <- data.table(iris)
dt[Sepal.Length >= 5.5 & Species == "setosa" | Species != "setosa"]

#>      Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
#>   1:          5.8         4.0          1.2         0.2    setosa
#>   2:          5.7         4.4          1.5         0.4    setosa
#>   3:          5.7         3.8          1.7         0.3    setosa
#>   4:          5.5         4.2          1.4         0.2    setosa
#>   5:          5.5         3.5          1.3         0.2    setosa
#>  ---                                                            
#> 101:          6.7         3.0          5.2         2.3 virginica
#> 102:          6.3         2.5          5.0         1.9 virginica
#> 103:          6.5         3.0          5.2         2.0 virginica
#> 104:          6.2         3.4          5.4         2.3 virginica
#> 105:          5.9         3.0          5.1         1.8 virginica

CodePudding user response：

You can use the | or operator:

This is asking to remove any lines where Species=="setosa" & Sepal.Length<5.5 and keep lines where Sepal.Length>5.5

iris1[!(Species=="setosa" & Sepal.Length<5.5) | Sepal.Length>5.5]

     Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
  1:          5.8         4.0          1.2         0.2    setosa
  2:          5.7         4.4          1.5         0.4    setosa
  3:          5.7         3.8          1.7         0.3    setosa
  4:          5.5         4.2          1.4         0.2    setosa
  5:          5.5         3.5          1.3         0.2    setosa
 ---                                                            
101:          6.7         3.0          5.2         2.3 virginica
102:          6.3         2.5          5.0         1.9 virginica
103:          6.5         3.0          5.2         2.0 virginica
104:          6.2         3.4          5.4         2.3 virginica
105:          5.9         3.0          5.1         1.8 virginica