We often need to group a data according to a certain attribute , Then calculate some statistics . stay R In language ,aggregate Function .
## S3 method for class 'data.frame' aggregate(x, by, FUN, ... simplify =
TRUE, drop = TRUE)
The parameters we often use are ：x, by, FUN.
x, The property or column you want to calculate .
by, It's a list, You can specify one or more columns as the basis for grouping .
FUN, Specify a function , Used to calculate , It can be applied to all grouped data .

If this is our data .
type<-c("a","b","c","a","c","d","b","a","c","b") value<-c(53,15,8,99,76,22,46,
56,34,54) df<-data.frame(type,value) df type value 1 a 53 2 b 15 3 c 8 4 a 99 5
c76 6 d 22 7 b 46 8 a 56 9 c 34 10 b 54
Group sum
aggregate(df\$value, by=list(type=df\$type),sum) type x 1 a 208 2 b 115 3 c 118
4 d 22
Group average
It's easy to average by groups , Just put the top sum Change to mean That's it .
aggregate(df\$value, by=list(type=df\$type),mean) type x 1 a 69.33333 2 b
38.33333 3 c 39.33333 4 d 22.00000
Group count , Group counting is statistics in the case of grouping rows Number of .
aggregate(df\$value, by=list(type=df\$type),length) type x 1 a 3 2 b 3 3 c 3 4 d
1
Group summation based on multiple attributes .
We add a column to the original data , Let's look at multi-attribute grouping .
type_2 <-c("F","M","M","F","F","M","M","F","M","M") df <- data.frame(df, type_2
) df type value type_2 1 a 53 F 2 b 15 M 3 c 8 M 4 a 99 F 5 c 76 F 6 d 22 M 7 b
46 M 8 a 56 F 9 c 34 M 10 b 54 M aggregate(x=df\$value, by=list(df\$type,df\$type_2
),sum) Group.1 Group.2 x 1 a F 208 2 c F 76 3 b M 115 4 c M 42 5 d M 22

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