Chao Liu - 5 months ago 13

R Question

I have a matrix in which each element is a pure categorical variable "a","b","c","d",... Each column of the matrix is a chronological entry and now I want to plot the matrix by row and I hope the y-axis is the sequence of characters.

Here is the original matrix:

Here is what I wanted the plot to be:

The red plot is first row of the matrix and the blue plot is the fifth.

I have tried some existing packages but mostly they require me to transfer the categorical variables to numerical variables. So I wonder if anyone could help me with this. Many thanks!

Answer

Without your data, I have to generate some toy one, called `mat`

, with 5 rows and 10 columns, filled with `letters[1:7]`

.

```
set.seed(0); mat <- matrix(sample(letters[1:7], 5 * 10, TRUE), nrow = 5)
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
#[1,] "g" "b" "a" "f" "f" "b" "c" "f" "c" "d"
#[2,] "b" "g" "b" "d" "g" "c" "d" "e" "f" "f"
#[3,] "c" "g" "b" "f" "b" "a" "e" "f" "e" "a"
#[4,] "e" "e" "e" "g" "e" "c" "d" "a" "f" "d"
#[5,] "g" "e" "c" "c" "a" "g" "b" "f" "d" "f"
```

Basically you need first re-represent you character matrix `mat`

with integers.

```
## flatten your object into a vector first
if (is.matrix(mat)) v <- as.character(mat)
if (is.data.frame(mat)) v <- as.character(unlist(mat, use.names = FALSE))
lev <- sort(unique(v)) ## sorted unique labels
## re-representation
mat_int <- matrix(match(v, lev), nrow = nrow(mat))
## or: mat_int <- matrix(as.integer(factor(v, levels = lev)), nrow = nrow(mat))
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
#[1,] 7 2 1 6 6 2 3 6 3 4
#[2,] 2 7 2 4 7 3 4 5 6 6
#[3,] 3 7 2 6 2 1 5 6 5 1
#[4,] 5 5 5 7 5 3 4 1 6 4
#[5,] 7 5 3 3 1 7 2 6 4 6
```

Then you just plot (the whole or some rows of) this matrix using `matplot`

. Disable the y-axis first then add it later using `axis`

so that you can customize axis labels.

```
## this plots the whole matrix
matplot(t(mat_int), yaxt = "n", type = "l", xlab = "time", ylab = "category")
axis(2, seq_along(lev), labels = lev)
## this plots 1st and 5th rows
matplot(t(mat_int)[, c(1,5)], yaxt = "n", type = "l", xlab = "time", ylab = "category")
axis(2, seq_along(lev), labels = lev)
```

Plot of the selected two rows: