Creating matrix and vector from csv or xlsx file

[ziachowdhury]

I want to create a matrix/vector from csv and xlsx files without titles at rows and columns. Also, I want to create a diagonal vector ( similar to diag (X) command in MATLAB) from xlsx file without title cell value. I would be glad if anyone helps me with the syntax for these purposes.
The following illustrates the xlsx file from which I want to create matrix and vector.

[FJCC]

Here is a simple example of importing a csv with row and column names and converting it to a matrix and also making a diagonal matrix.

df <- read.csv("C:\\Users\\fjcc\\Documents\\R\\Play\\Dummy.txt")
df
#>       A  B  C
#> row1 10 11 12
#> row2 20 21 22
#> row3 30 31 32
MAT <- as.matrix(df)
MAT
#>       A  B  C
#> row1 10 11 12
#> row2 20 21 22
#> row3 30 31 32
dimnames(MAT) <- list(NULL, NULL) #if you do not want the  names
MAT
#>      [,1] [,2] [,3]
#> [1,]   10   11   12
#> [2,]   20   21   22
#> [3,]   30   31   32

DiagMat <- diag(MAT[, 1]) #make a diagonal matrix from the first column of MAT
DiagMat
#>      [,1] [,2] [,3]
#> [1,]   10    0    0
#> [2,]    0   20    0
#> [3,]    0    0   30

^{Created on 2019-02-28 by the reprex package (v0.2.1)}

[ziachowdhury]

Hey FJCC,
I am glad you replied. However, it doesn't work since my xlsx file contains multiple sheets. how to define sheet for read.csv function? Thank you

[Yarnabrina]

If you have a xlsx file, you can't use read.csv. Use one these packages: readxl, xlsx, openxlsx.