我有这样的data.table
dput(DT)
structure(list(ref = c(3L, 3L, 3L, 3L), nb = 12:15, i1 = c(3.1e-05,
0.044495, 0.82244, 0.322291), i2 = c(0.000183, 0.155732, 0.873416,
0.648545), i3 = c(0.000824, 0.533939, 0.838542, 0.990648), i4 = c(0.044495,
0.82244, 0.322291, 0.393595)), .Names = c("ref", "nb", "i1",
"i2", "i3", "i4"), row.names = c(NA, -4L), class = c("data.table",
"data.frame"), .internal.selfref = <pointer: 0x0000000000320788>)
DT
# ref nb i1 i2 i3 i4
# 1: 3 12 0.000031 0.000183 0.000824 0.044495
# 2: 3 13 0.044495 0.155732 0.533939 0.822440
# …