如何选取R中每个整数的100个样例?

Question

我需要从mnist数据库中选择每个数字的100个示例(因此100个零，100个一，100个二，等等)，我该怎么做呢?我已经试过了，但就是找不到方法。

Answer 1

library("keras")
library("dplyr")
#choosing just training data
mnist<-dataset_mnist()
train_images = mnist$train$x
train_labels = mnist$train$y
#prepear list for labels and 1000*28*28 array for images
mnist_labels=c()
mnist_images<-array(0,dim=c(1000,28,28))
i=1
for (x in 0:9){
#find first 100 x labels and save indexes in tempList, later append mnist_label list, mnist_images array with it
tempList=which(train_labels %in% x)%>%head(100)
for (y in tempList){
mnist_labels[i]<-train_labels[y]
mnist_images[i,1:28,1:28]<-train_images[y,1:28,1:28]
i=i+1
}
}
rm(x,y,i)
#Visualize 1th digit
first_digit<- mnist_images[1, 1:28, 1:28]
par(pty="s")
image(t(first_digit), col = gray((0:255)/255), axes= FALSE)
# visualize first 100 digits ( all zeros) if you want to get eg last 100 ( all nines, change under for loop both index with index+900)
par(mfcol=c(10,10))
par(mar=c(0, 1, 1, 0), xaxs='i', yaxs='i')
for (index in 1:100) { 
im <- mnist_images[index,,]
im <- t(apply(im, 2, rev)) 
image(1:28, 1:28, im, col=gray((0:255)/255), 
xaxt='n', main=paste(mnist_labels[index]),axes= FALSE)
}
rm(index)