项目计数描述性统计

Question

我有一个数据框

x  userId  bookId  rating
1       1     412       6
2       1     454       5
3       2     412       4

等等..

基本上,用户已经评价了许多书籍,并且书籍具有许多评级.

我需要提取一些描述性统计数据userId.平均评级数量,平均评级等.

有谁能指出我正确的方向？

Answer 1

您可以使用以下命令进行以下计算data.table:

如果你data.frame被称为books:

require(data.table)
setDT(books)

# average rating by user
books[, mean(rating), by=userId]
#   userId  V1
#1:      1 5.5
#2:      2 4.0

# average amount of ratings given :
books[, .N, by=userId][, mean(N)]
#[1] 1.5

Answer 2

我不确定我是否得到您的确切问题/任务.但以下内容可以提供一些见解:

data = read.table(header = T, stringsAsFactors = F,  text  = "x  userId  bookId  rating
1       1     412       6
2       1     454       5
3       2     412       4")

# Number of ratings per user 
userFreq = data.frame(table(data$userId)) 
# Var1 Freq
# 1    1    2
# 2    2    1

# mean rating per userID
meanRatingPerUser = aggregate(data$rating, by=list(data$userId), FUN = mean )     
# Group.1   x
# 1       1 5.5
# 2       2 4.0

# mean rating per book
meanRatingPerBook = aggregate(data$rating, by=list(data$bookId), FUN = mean )   
# Group.1 x
# 1     412 5
# 2     454 5


# "Summary" function, applied per bookID
moreStats = aggregate(data$rating, by=list(data$bookId), FUN = summary ) 
# Group.1 x.Min. x.1st Qu. x.Median x.Mean x.3rd Qu. x.Max.
# 1     412    4.0       4.5      5.0    5.0       5.5    6.0
# 2     454    5.0       5.0      5.0    5.0       5.0    5.0