More descriptive stratify errors.

[syntagmatic]

This would be especially helpful to people using d3-stratify for the first time, such as forking an example like Tidy Tree and trying to input their own data.

Some ideas about what the text might be.

• d3-stratify: cannot accept multiple root nodes
• d3-stratify: requires a root node to create a valid hierarchy
• d3-stratify: this parent id is missing from the hierarchy: nodeId
• d3-stratify: ambiguous reference: nodeId matches two parents

[mbostock]

d3-stratify already outputs descriptive errors:

• "multiple roots"
• "missing: " + nodeId
• "ambiguous: " + nodeId
• "no root"
• "cycle"

I think that plus the stack trace and documentation should be sufficient.

[tylergraf]

I couldn't figure out what ambiguous meant. Thanks @syntagmatic, this really helped my debugging.

[joar]

@mbostock Except when you're running with minified D3. I just had this issue, with "missing:".

I thought it was the CSV parsing before I found this Issue. At least a d3-stratify: missing: $foo would be nice, in the minified case.

[herebebeasties]

It would be really, really nice if it told you what was causing the cycle, though - Error("cycle") isn't very helpful when you have 1000 nodes in your "tree".

[schindld]

It would be really, really nice if it told you what was causing the cycle, though - Error("cycle") isn't very helpful when you have 1000 nodes in your "tree".

I'm stuck on the Error: cycle error right now with a dataset of 27811 nodes...Such a useless error message. At least output the relevant nodes' ids.