I have a list of names in column A, with corresponding numbers in column B

There are many different names in A that repeat over and over.
I would like to calculate the StDev for the column B values for each unique name.

This is what I'm trying to create: StdevIF(A="JimBob",B:B)

I don't think there is a way to do this with the Stdev function, but one can calculate the standard deviation manually in the cell. This is what I've come up with, where C3 = "JimBob"
=SQRT(SUMPRODUCT(--(A$2:A$1048576=C3),(B$2:B$1048576)-AVERAGEIF(A$2:A$1048576,C3,B$2:B$1048576)^2)/COUNTIF(A$2:A$1048576,C3))

but it is not returning the same value as STDEV does when I isolate JimBob's numbers and use the STDev function. I don't know if this is because I'm manually calculating the SD wrong, or I've made a mistake in my syntax. Any help would be greatly appreciated.
-Paul