no implicit conversion from nil to integer - when trying to add anything to array - ruby

Question

I'm trying to build a fairly complex hash and I am strangely getting the error
no implicit conversion from nil to integer
when I use the line
manufacturer_cols << {:field => 'test'}
I use the same line later in the same loop, and it works no problem.
The entire code is
manufacturer_cols=[]
manufacturer_fields.each_with_index do |mapped_field, index|
if mapped_field.base_field_name=='exactSKU'
#this is where it is breaking, if I comment this out, all is good
manufacturer_cols << { :base_field=> 'test'}
else
#it works fine here!
manufacturer_cols << { :base_field=>mapped_field.base_field_name }
end
end
------- value of manufacturer_fields --------
[{"base_field":{"base_field_name":"Category","id":1,"name":"Category"}},{"base_field":{"base_field_name":"Description","id":3,"name":"Short_Description"}},{"base_field":{"base_field_name":"exactSKU","id":5,"name":"Item_SKU"}},{"base_field":{"base_field_name":"Markup","id":25,"name":"Retail_Price"}},{"base_field":{"base_field_name":"Family","id":26,"name":"Theme"}}]

Answer 1

Implicit Conversion Errors Explained
I'm not sure precisely why your code is getting this error but I can tell you exactly what the error means, and perhaps that will help.
There are two kinds of conversions in Ruby: explicit and implicit.
Explicit conversions use the short name, like #to_s or #to_i. These are commonly defined in the core, and they are called all the time. They are for objects that are not strings or not integers, but can be converted for debugging or database translation or string interpolation or whatever.
Implicit conversions use the long name, like #to_str or #to_int. This kind of conversion is for objects that are very much like strings or integers and merely need to know when to assume the form of their alter egos. These conversions are never or almost never defined in the core. (Hal Fulton's The Ruby Way identifies Pathname as one of the classes that finds a reason to define #to_str.)
It's quite difficult to get your error, even NilClass defines explicit (short name) converters:
nil.to_i
=> 0
">>#{nil}<<" # this demonstrates nil.to_s
=> ">><<"
You can trigger it like so:
Array.new nil
TypeError: no implicit conversion from nil to integer
Therefore, your error is coming from the C code inside the Ruby interpreter. A core class, implemented in C, is being handed a nil when it expects an Integer. It may have a #to_i but it doesn't have a #to_int and so the result is the TypeError.

Answer 2

This seems to have been completely unrelated to anything that had anything to do with manufacturer_cols after all.
I had arrived at the manufacturer_cols bit because if I commented that out, it ran fine.
However, if I commented out the part where I ran through the csv further down the page, it ran fine also.
It turns out the error was related to retrieving attempting to append the base_field when it was nil.
I thought I could use
manufacturer_cols.each do |col|
base_value = row[col[:row_index].to_i]
if col[:merges]
col[:merges].each do |merge|
base_value += merge[:separator].to_s + row[merge[:merge_row_index]]
end
end
end
unfortunately, that caused the error. the solution was
base_value = base_value + merge[:separator].to_s + row[merge[:merge_row_index]]
I hope this helps somebody, 'cause as DigitalRoss alluded to, it was quite a wild goose chase nailing down where in the code this was being caused and why.

Answer 3

I got this error when parsing through an API for "tag/#{idnum}/parents"...Normally, you'd expect a response like this:
{
"parents": [
{
"id": 8,
"tag_type": "MarketTag",
"name": "internet",
"display_name": "Internet",
"angellist_url": "https://angel.co/internet",
"statistics": {
"all": {
"investor_followers": 1400,
"followers": 5078,
"startups": 13214
},
"direct": {
"investor_followers": 532,
"followers": 1832,
"startups": 495
}
}
}
],
"total": 1,
"per_page": 50,
"page": 1,
"last_page": 1
}
but when I looked up the parents of the market category "adult" (as it were), I got this
{
"parents": [ ],
"total": 0,
"per_page": 50,
"page": 1,
"last_page": 0
}
Now ruby allowed a number of interactions with this thing to occur, but eventually it threw the error about implicit conversion
parents.each do |p|
stats = p['statistics']['all']
selector << stats['investor_followers'].to_i
end
selected = selector.index(selector.max)
parents[selected]['id'] ***<--- CODE FAILED HERE
end

Answer 4

This was a simple fix for me.
When I was getting this error using the Scout app, one of my mapped folders was header-1, when I removed the hyphen from the folder name and made it header1, the error went away.
It didn't like the hyphen for some reason...