Load the MNIST digit recognition dataset with R and see any results - r

Question

In the book "Machine Learning - A Probabilistic Perspective" by Kevin P. Murphy the first task reads:
Exercise 1.1 KNN classifier on shuffled MNIST data
Run mnist1NNdemo
and verify that the misclassification rate (on the first 1000 test
cases) of MNIST of a 1-NN classifier is 3.8%. (If you run it all on
all 10,000 test cases, the error rate is 3.09%.) Modify the code so
that you first randomly permute the features (columns of the training
and test design matrices), as in shuffledDigitsDemo, and then apply
the classifier. Verify that the error rate is not changed.
My simple understanding is that the exercise is looking for the 1-NN after loading the files(kNN() in R).
The files:
train-images-idx3-ubyte.gz: training set images (9912422 bytes)
train-labels-idx1-ubyte.gz: training set labels (28881 bytes)
t10k-images-idx3-ubyte.gz: test set images (1648877 bytes)
t10k-labels-idx1-ubyte.gz: test set labels (4542 bytes)
are taken from the The MNIST DATABASE
I found a popular template for loading the files:
# for the kNN() function
library(VIM)
load_mnist <- function() {
load_image_file <- function(filename) {
ret = list()
f = file(filename,'rb')
readBin(f,'integer',n=1,size=4,endian='big')
ret$n = readBin(f,'integer',n=1,size=4,endian='big')
nrow = readBin(f,'integer',n=1,size=4,endian='big')
ncol = readBin(f,'integer',n=1,size=4,endian='big')
x = readBin(f,'integer',n=ret$n*nrow*ncol,size=1,signed=F)
ret$x = matrix(x, ncol=nrow*ncol, byrow=T)
close(f)
ret
}
load_label_file <- function(filename) {
f = file(filename,'rb')
readBin(f,'integer',n=1,size=4,endian='big')
n = readBin(f,'integer',n=1,size=4,endian='big')
y = readBin(f,'integer',n=n,size=1,signed=F)
close(f)
y
}
train <<- load_image_file("train-images.idx3-ubyte")
test <<- load_image_file("t10k-images.idx3-ubyte")
train$y <<- load_label_file("train-labels.idx1-ubyte")
test$y <<- load_label_file("t10k-labels.idx1-ubyte")
}
show_digit <- function(arr784, col=gray(12:1/12)) {
image(matrix(arr784, nrow=28)[,28:1], col=col)
}
According to the comment, in the command line this should work:
# Error "Error in matrix(arr784, nrow = 28) : object 'train' not found"
show_digit(train$x[5,])
The question is how can I use the show_digit function ?
Edit Remove extra question

Answer 1

What I figured out for the problem:
First run the whole file in R Studio or ESS, then call the load_mnist() from the console.
After that execute show_digit(train$x[3,]) in the console again and it works.
Finding the KNN classifier can be done on the whole data set:
a <- knn(train, test, train$y) but it would be a very slow process.
Predictions for the result can be done like table(test$y, a), test$y is predicted, a is the actual result.