Cannot read property '0' of null in clipCells()

[brianwebb11]

I'm using d3 4.2.2. I'm getting an exception in clipCells().

angular.js:13920 TypeError: Cannot read property '0' of null
    at clipCells (d3.js:11482)
    at new Diagram (d3.js:11849)
    at voronoi (d3.js:11918)
    at Function.voronoi.polygons (d3.js:11927)
    ...

Looking at the code it appears that the variable end is referenced end[0] before it is populated with a value.

https://github.com/d3/d3-voronoi/blob/master/src/Cell.js#L75

I don't have a simple test case right now since I'm seeing this exception buried under several other layers of 3rd party code that ends up calling d3.

Thanks for having a look.

[mbostock]

I’d like to look into this, but without a test case that reproduces the error, I’m not sure where to start.

[brianwebb11]

I discovered there was a problem in an intermediate library which calls into d3. The problem was that the other library defined a callBack() function in d3.voronoi().y(callBack). The callBack() function would sometime return data that was incorrect.

Sorry for the confusion.

[mbostock]

Thanks for letting me know.

[micahstubbs]

also experiencing just this issue. it's also hard for me to reproduce the error with the same data in a single page example.

[micahstubbs]

@brwebb do you remember how your data was sometimes incorrect?

[micahstubbs]

here's a working example with the exact data that fails in my larger project http://bl.ocks.org/micahstubbs/2e7c882e69aa10d9dc317b59baf64692

now to go figure out if something is transforming the data in the middle of the larger project before it gets to d3.voronoi() 💭

[brianwebb11]

Unfortunately I don't remember the details. However, I think it had something to do with processing data points where the x or y value did not exist, maybe 0 or null.

[micahstubbs]

@brwebb, thanks all the same! it looks like sparse data with lots of 0 values is the issue for me

[micahstubbs]

@mbostock managed to make a minimal example that reproduces the issue
Voronoi clipCells() end[1] null Example II

this second example, though less minimal, logs out internal values from d3 to the console to perhaps shed some light on the error message
Voronoi clipCells() end[1] null Example III

[micahstubbs]

it looks like this could be the cause #12

thanks to @Fil for the answer over on slack

[micahstubbs]

for voronoi you're not allowed to have two points at the same coords

[AlexanderBollbach]

i'm also seeing this error in the same clipCells function. have spent many hours on this and made no progress

[micahstubbs]

@AlexanderBollbach is there a minimal example of the place you experience the error that you can share?

(nice to see others encounter this same specific issue as I did 😄 )