Question

我正在尝试从R中的matrix填充dataframe

# A demo Data Frame
d = data.frame(movie=c(1,2,3),user=c(1,3,2),rating=c(1,4,2))
# Initialize Output Matrix
output<-matrix(data=NA,nrow = length(d$movie),ncol = length(d$user),byrow = FALSE,)


#Function 
# x= movie, y = user, input=data frame to be indexed, out = output matrix
getMatrixFilled<-function(x,y,input,out){
      out[x,y]<-input[x,y];
      out
    }

我想采用movie，user和相应的rating并将其置于矩阵

as

 output[movie,user]<-rating

提前感谢您的帮助!!

输入

> d
  movie user rating
1     1    1      1
2     2    3      4
3     3    2      2

所需输出

> outputM
     [,1] [,2] [,3]
[1,]    1   NA   NA
[2,]   NA   NA    4
[3,]   NA    2   NA

Answer 1

你可以尝试

output[as.matrix(d[1:2])] <- d$rating
output
#     [,1] [,2] [,3]
#[1,]    1   NA   NA
#[2,]   NA   NA    4
#[3,]   NA    2   NA

Answer 2

我怀疑你想要一个简单的重塑：

library(reshape2)
acast(d, movie ~ user)
#   1  2  3
#1  1 NA NA
#2 NA NA  4
#3 NA  2 NA

Answer 3

由于我们正在猜测所需的输出，因此以下是其他几种与现有答案类似的替代方案：

xtabs(rating ~ movie + user, d)
#      user
# movie 1 2 3
#     1 1 0 0
#     2 0 0 4
#     3 0 2 0

library(tidyr)
spread(d, user, rating)
#   movie  1  2  3
# 1     1  1 NA NA
# 2     2 NA NA  4
# 3     3 NA  2 NA

并且（根据大众需求），基础R reshape（但列的排序方式不同）......

reshape(d, direction = "wide", idvar = "movie", timevar = "user")
#   movie rating.1 rating.3 rating.2
# 1     1        1       NA       NA
# 2     2       NA        4       NA
# 3     3       NA       NA        2

Answer 4

我认为@akrun向您展示了最简单的方法。（你几乎就在那里。但索引需要以矩阵的形式传递给"["。）我发布了使用双列矩阵的应用程序，用于将分配索引到矩阵位置的格式为你要求的功能。

 d = data.frame(movie=c(1,2,3),user=c(1,3,2),rating=c(1,4,2))

 output<-matrix(data=NA,nrow = length(d$movie),ncol = length(d$user) )
 getMatrixFilled<-function(x,y,input,out){
       out[cbind(x,y)] <- input[ , "rating"]
       out
     }
 getMatrixFilled(x=d$movie, y=d$user , input=d, out=output)
#--------------
     [,1] [,2] [,3]
[1,]    1   NA   NA
[2,]   NA   NA    4
[3,]   NA    2   NA

R编程：数据帧到矩阵的转换

4 个答案: