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"how to read mnist database in r?" Code Answer

endian="big", not "high":

> to.read = file("~/downloads/t10k-images-idx3-ubyte", "rb")

magic number:

> readbin(to.read, integer(), n=1, endian="big")
[1] 2051

number of images:

> readbin(to.read, integer(), n=1, endian="big")
[1] 10000

number of rows:

> readbin(to.read, integer(), n=1, endian="big")
[1] 28

number of columns:

> readbin(to.read, integer(), n=1, endian="big")
[1] 28

here comes the data:

> readbin(to.read, integer(), n=1, endian="big")
[1] 0
> readbin(to.read, integer(), n=1, endian="big")
[1] 0

as per the training set image data description on the web site.

now you just need to loop and read 28*28 byte chunks into matrices.

start again:

 > to.read = file("~/downloads/t10k-images-idx3-ubyte", "rb")

skip header:

> readbin(to.read, integer(), n=4, endian="big")
[1]  2051 10000    28    28

should really get the 28,28 from the header read but hard-coded here:

 > m = matrix(readbin(to.read,integer(), size=1, n=28*28, endian="big"),28,28)
 > image(m)

might need to transpose or flip the matrix, i think its an upside-down "7".

par(mfrow=c(5,5))
par(mar=c(0,0,0,0))
for(i in 1:25){m = matrix(readbin(to.read,integer(), size=1, n=28*28, endian="big"),28,28);image(m[,28:1])}

gets you:

oh, and google leads me to: http://www.inside-r.org/packages/cran/darch/docs/readmnist which might be useful.

By Soufiane Boutahlil on February 18 2022

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