Here's an example with no data file:

DL> fuv_nrows=13582379

GDL> fuv=fltarr(5,fuv_nrows)

GDL> fuv(0,*) = lindgen(fuv_nrows) mod 1300

GDL> h=histogram(fuv(0,*),min=0,bin=1)

GDL> help,h

H LONG = Array[1300]

GDL> for i=0,1299 do t(i)=n_elements(where(fuv(0,*) eq i))

GDL> q=where(h ne t)

GDL> print,q(0)

2

GDL> print,h(0),t(0)

10448 10448

GDL> print,h(2),t(2)

20896 10448