According to Mother Jones's editor there have been only four.
"There's been nowhere near 355 mass shootings in 2015, and according to Mother Jones editor Mark Folman, there have been exactly four.
At Mother Jones, where I work as an editor, we have compiled an
in-depth, open-source database covering more than three decades of public mass shootings. By our measure, there have been four “mass shootings” this year, including the one in San Bernardino, and at least 73 such attacks since 1982.
What explains the vastly different count? The answer is that there is no official definition for “mass shooting.” Almost all of the gun crimes behind the much larger statistic are less lethal and bear little relevance to the type of public mass murder we have just witnessed again. Including them in the same breath suggests that a 1 a.m. gang fight in a Sacramento restaurant, in which two were killed and two injured, is the same kind of event as a deranged man walking into a community college classroom and massacring nine and injuring nine others. Or that a late-night shooting on a street in Savannah, Ga., yesterday that injured three and killed one is in the same category as the madness that just played out in Southern California.
While all the victims are important, conflating those many other crimes with indiscriminate slaughter in public venues obscures our understanding of this complicated and
growing problem. Everyone is desperate to know why these attacks happen and how we might stop them — and we can’t know, unless we collect and focus on useful data that filter out the noise."
No, there haven't been 355 'mass shootings' this year
