non-numeric argument binary operator error - r

Question

Not sure why I am getting a non-numeric argument binary operator error. Do I have some type mismatch going on?
for (j in 1:length(theta)) {
val = exp(y * sum(theta * random_data_vector) * y * random_data_vector[i])
val = val / (1 + exp(y * sum(theta * random_data_vector)))
theta[j] = theta[j] - (alpha * val)
}
Error:
Error in theta * random_data_vector :
non-numeric argument to binary operator
Values:
> head(theta)
[1] 0.02435863 -0.74310189 -0.63525839 0.56554085 -0.20599967 0.43164130
> head(random_data_vector)
[1] 0 0 0 0 0 0
> y
V9437
785 1
After FIRST iteration of for loop, theta looks like this:
> head(theta)
[[1]]
[1] NA
[[2]]
[1] -0.2368957
[[3]]
[1] 0.697332
[[4]]
[1] 0.6104201
[[5]]
[1] 0.8182983
[[6]]
[1] 0.7093492
For more information, the above is a snippet from my entire function I am trying to create around stochastic gradient descent.
data is a set of rows grabbed from a CSV
labels is 1 row grabbed from a CSV
alpha is a float
mnist = read.csv('mnist_train.csv', header=FALSE)
data = mnist[,mnist[nrow(mnist),]==0 | mnist[nrow(mnist),]==1, drop=FALSE]
labels = data[785,]
data = data[1:784,]
train = function(data, labels, alpha) {
theta = runif(nrow(data),-1,1)
decay_rate = .01
random_column_indexes = sample(ncol(data))
idx = 1
limit = length(random_column_indexes)
threshold = 1e-5
delta = 1000000
for (n in 1:ncol(data)) {
if (delta <= threshold) {
break
}
i = random_column_indexes[n]
random_data_vector = data[, i]
y = labels[i]
previous_theta = theta
for (j in 1:length(theta)) {
val = exp(y * sum(theta * random_data_vector) * y * random_data_vector[i])
val = val / (1 + exp(y * sum(theta * random_data_vector)))
theta[j] = theta[j] - (alpha * val)
}
alpha = alpha - decay_rate
delta = abs(previous_theta - theta)
}
return(theta)
}

Answer 1

I consider that the problem has to do with the subsetting of your objects. From the link you provided in the comments I see that your data is a data.frame object and you subset it using [. If you check the type of any data.frame e.g. typeof(iris) you can see that it is a "list".
When you use y = labels[i], your object will be a list, that's because:
when [ is applied to a list it always returns a list: it never gives you the contents of the list. To get the contents, you need [[ Advanced R by Hadley Wickham
Declare y as y <- labels[[i]] or subset labels from your data.frame as a vector doing as.numeric(data[785,])