Stddev function accepts strings

[Tomcat-Engineering]

This line in the source code specifically allows the stddev (standard deviation) function to accept time series of datatype "string".

Obviously there is no sensible way to take the standard deviation of a load of strings, and the implementation always returns an empty string.

This is inconsistent with all the other comparable functions (such as mean), which throw an error if you feed them strings.

Was there a reason for this special case?

[jsternberg]

Looks like the piece of code that allows stddev() to operate on strings has been there since the beginning and I can't find a commit that explains why from a quick look.

@benbjohnson do you have any idea?

[benbjohnson]

@jsternberg I can't think of any reason to use a string. We can remove that.