视频为何无法观看

已经登录，观看视频时，扔提示“请登录后播放”，不知是什么问题

安装成功后，尝试按照课程3操作，但是出现以下信息错误 > mat_a Error: object 'mat_a' not found WARNING: You are configured to use the CRAN mirror at https://cran.rstudio.com/. This mirror supports secure (HTTPS) downloads however your system is unable to communicate securely with the server (possibly due to out of date certificate files on your system). Falling back to using insecure URL for this mirror.

①数据框 df -data.frame(k=1:3,y=c("a","b","c"),z=0) ②转换成矩阵df_1 -as.matrix(df)后，数据类型全部变为chr型；③再转换成数据框df_2 -as.data.frame(df_1) ，数据类型全部变为factor型

转换成矩阵后，数据类型全部变为字符（chr）型；再将这一矩阵转换为数据框后，数据类型全部变为factor型。 ``` > x - data.frame(a=1:3, b=c('A', T, F), c=0) > x a b c 1 1 A 0 2 2 TRUE 0 3 3 FALSE 0 > y - as.matrix(x) > y a b c [1,] "1" "A" "0" [2,] "2" "TRUE" "0" [3,] "3" "FALSE" "0" > z - as.data.frame(y) > z a b c 1 1 A 0 2 2 TRUE 0 3 3 FALSE 0 > str(z) 'data.frame': 3 obs. of 3 variables: $ a: Factor w/ 3 levels "1","2","3": 1 2 3 $ b: Factor w/ 3 levels "A","FALSE","TRUE": 1 3 2 $ c: Factor w/ 1 level "0": 1 1 1 ```

安装成功后，尝试按照课程3操作，但是出现以下信息错误 > mat_a Error: object 'mat_a' not found WARNING: You are configured to use the CRAN mirror at https://cran.rstudio.com/. This mirror supports secure (HTTPS) downloads however your system is unable to communicate securely with the server (possibly due to out of date certificate files on your system). Falling back to using insecure URL for this mirror.

视频为何无法观看

很好课程！！！