Create dataframe from a matrix

dataframe, matrix, r

Solution

If you change your `time` column into row names, then you can use `as.data.frame(as.table(mat))` for simple cases like this.

Example:

data <- c(0.1, 0.2, 0.3, 0.3, 0.4, 0.5)
dimnames <- list(time=c(0, 0.5, 1), name=c("C_0", "C_1"))
mat <- matrix(data, ncol=2, nrow=3, dimnames=dimnames)
as.data.frame(as.table(mat))
  time name Freq
1    0  C_0  0.1
2  0.5  C_0  0.2
3    1  C_0  0.3
4    0  C_1  0.3
5  0.5  C_1  0.4
6    1  C_1  0.5

In this case time and name are both factors. You may want to convert time back to numeric, or it may not matter.

Problem

How to get a data frame with the same data as an already existing matrix has? A simplified example of my matrix: ``` mat <- matrix(c(0, 0.5, 1, 0.1, 0.2, 0.3, 0.3, 0.4, 0.5), ncol = 3, nrow = 3, dimnames = list(NULL, c("time", "C_0", "C_1"))) > mat time C_0 C_1 [1,] 0.0 0.1 0.3 [2,] 0.5 0.2 0.4 [3,] 1.0 0.3 0.5 ``` I would like to create a data frame that looks like this: ``` name time val 1 C_0 0.0 0.1 2 C_0 0.5 0.2 3 C_0 1.0 0.3 4 C_1 0.0 0.3 5 C_1 0.5 0.4 6 C_1 1.0 0.5 ``` All my attempts are quite clumsy, for example: ``` data.frame(cbind(c(rep("C_1", 3), rep("C_2", 3)), rbind(cbind(mat[,"time"], mat[,"C_0"]), cbind(mat[,"time"], mat[,"C_1"])))) ``` Does anyone have an idea of how to do this more elegantly? Please note that my real data has a few more columns (40 columns).

Original source