How to find the absolute maximum of each group in data.table object in R?

To find the absolute maximum of each group in data.table object in R, we can follow the below steps −

• First of all, create a data.table object.

• Then, use summarise_each function of dplyr package along with which.max and abs function to find the absolute maximum of each group after grouping with group_by.

Example 1

Create the data.table object

Let’s create a data.table object as shown below −

library(data.table) Class<-sample(c("I","II","III"),25,replace=TRUE) Response<-sample(-50:50,25) DT1<-data.table(Class,Response) DT1

Output

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

   Class Response 1:   II     25 2:    I   -29 3:   II     14 4:  III     35 5:  III    -3 6:    I    -10 7:  III    -22 8:  III    -28 9:   II    -15 10:   I    -41 11:   I   -8 12:  III   -1 13:   II   -11 14:   II 9 15:  III 45 16:   II -23 17:    I 42 18:   II -16 19:  III 44 20:   II -47 21:  III 37 22:  III -27 23:    I -40 24:    I 18 25:   II 3     Class Response

Find the absolute maximum of each group

Using summarise_each function of dplyr package along with which.max and abs function to find the absolute maximum of each group for column Response after grouping with group_by as shown below −

library(data.table) Class<-sample(c("I","II","III"),25,replace=TRUE) Response<-sample(-50:50,25) DT1<-data.table(Class,Response) library(dplyr) DT1 %>% group_by(Class) %>% summarise_each(funs(.[which.max(abs(.))]))

Output

# A tibble: 3 x 2 Class Response <chr> <int> 1 I 42 2 II -47 3 III 45

Example 2

Create the data.table object

Let’s create a data.table object as shown below −

library(data.table) Factor<-sample(c("F1","F2","F3","F4","F5"),25,replace=TRUE) DV<-rnorm(25) DT2<-data.table(Factor,DV) DT2

Output

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

 Factor DV 1: F5 -2.17198942 2: F2 1.86828270 3: F5 -0.13921697 4: F1 -1.12527133 5: F2 0.30994193 6: F3 -0.85019956 7: F1 -0.53960590 8: F4 0.71515012 9: F1 0.95894780 10: F1 0.69673391 11: F1 1.59025968 12: F1 0.54539870 13: F2 1.03472636 14: F2 -0.86223774 15: F5 1.09875408 16: F5 0.76012240 17: F2 -0.81212071 18: F4 0.16992534 19: F4 0.15300303 20: F3 -1.16854925 21: F5 0.83239589 22: F5 -0.43753269 23: F4 0.03010316 24: F3 0.15060870 25: F5 -0.84028548 Factor DV

Find the absolute maximum of each group

Using summarise_each function of dplyr package along with which.max and abs function to find the absolute maximum of each group for column DV after grouping with group_by as shown below −

library(data.table) Factor<-sample(c("F1","F2","F3","F4","F5"),25,replace=TRUE) DV<-rnorm(25) DT2<-data.table(Factor,DV) library(dplyr) DT2 %>% group_by(Factor) %>% summarise_each(funs(.[which.max(abs(.))]))

Output

# A tibble: 5 x 2 Factor DV <chr> <dbl> 1 F1 1.59 2 F2 1.87 3 F3 -1.17 4 F4 0.715 5 F5 -2.17