r - 从R中的表中过滤记录

Question

我有一个数据集电影。

head(Movies)

如何获取 MovieID 为“0000008”的行？我努力了：

t1 = subset(Movies, "MovieID" == "0000008")
t2 <- Movies[ which(Movies["MovieID"]=="0000008"), ]
head(t1)
head(t2)

两者都返回空数据集，这是错误的，因为我可以看到 ID 为“0000008”的行。

编辑：我尝试从 MovieID 中删除“”，但这会引发错误：

子集.matrix（电影，MovieID ==“0000008”）中的错误：找不到对象'MovieID'

编辑：电影数据是这样获得的：

URL = "https://raw.githubusercontent.com/sidooms/MovieTweetings/master/latest/movies.dat"
MovieText = readLines( remote.file(URL) ) # HACK!!!
Movies = matrix( sapply( MovieText,
            function(x) unlist(strsplit(sub(" [(]([0-9]+)[)]", "::\\1",x),"::"))[1:4] ),
            nrow=length(MovieText), ncol=4, byrow=TRUE )
colnames(Movies) = c("MovieID", "MovieTitle", "Year", "Genres")

Answer 1

你nrow应该是length(MovieText)/4

URL = "https://raw.githubusercontent.com/sidooms/MovieTweetings/master/latest/movies.dat"
MovieText = readLines( URL ) # HACK!!!
Movies = matrix( sapply( MovieText,
    function(x) unlist(strsplit(sub(" [(]([0-9]+)[)]", "::\\1",x),"::"))[1:4] ),
    nrow=length(MovieText)/4, ncol=4, byrow=TRUE )
colnames(Movies) = c("MovieID", "MovieTitle", "Year", "Genres")

#if you want to work with matrix, then use this
subset(Movies, Movies[,"MovieID"]=="0000008")

编辑：data.frame和data.table子集

library(data.table)

MoviesDF <- data.frame(Movies)
MoviesDT <- data.table(Movies)

MoviesDF[MoviesDF["MovieID"] == "0000008", ]
MoviesDT[MovieID == "0000008", ]

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