R data.table binary OR across specific columns

Maybe you are willing to try (data.table version 1.14.3 for row-wise operation)

for (i in c('spr_1','spr_15','spr_99')) {
     DT[,(i) := max(.SD), .SDcols=patterns(paste0(i,"\\.")),by = .I]    
}

For stable data.table version,

for (i in c('spr_1','spr_15','spr_99')) {
     DT[,(i) := Reduce(pmax,.SD),.SDcols=patterns(paste0(i,"\\."))]    
}

P.S: It's better to use do.call to replace Reduce here. see @r2evans 's answer.

Formalizing my comments above into a benchmark. This is not a new answer (other than recommending do.call over Reduce, but that's not very novel), just an extended comment. (I'll delete it if it is too far out of context.)

DTbig <- rbindlist(replicate(1e7, DT, simplify=FALSE))
nrow(DTbig)
# [1] 40000000

Proof of the do.call(pmax, .SD) concept:

DTbig2 <- copy(DTbig)
for (i in c('spr_1','spr_15','spr_99')) {
  DTbig2[,(i) := Reduce(pmax, .SD), .SDcols = patterns(paste0(i, "\\."))]
}
for (i in c('spr_1','spr_15','spr_99')) {
  DTbig[,(i) := do.call(pmax, .SD), .SDcols = patterns(paste0(i, "\\."))]
}
identical(DTbig, DTbig2)
# [1] TRUE

Benchmark:

bench::mark(
orig = {
  for (i in c('spr_1','spr_15','spr_99')) {
    DTbig[,(i) := +Reduce(`|`, .SD), .SDcols = patterns(paste0(i, "\\."))]
  }
},
Reduce = {
  for (i in c('spr_1','spr_15','spr_99')) {
    DTbig[,(i) := Reduce(pmax,.SD), .SDcols=patterns(paste0(i,"\\."))]
  }
},
docall = {
  for (i in c('spr_1','spr_15','spr_99')) {
    DTbig[,(i) := do.call(pmax, .SD), .SDcols = patterns(paste0(i, "\\."))]
  }
}, iterations = 20)
# # A tibble: 3 x 13
#   expression      min   median `itr/sec` mem_alloc `gc/sec` n_itr  n_gc total_time result memory               time       gc       
#   <bch:expr> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl> <int> <dbl>   <bch:tm> <list> <list>               <list>     <list>   
# 1 orig       956.22ms    1.08s     0.939    2.68GB     2.35     6    15      6.39s <NULL> <Rprofmem [109 x 3]> <bench_tm~ <tibble ~
# 2 Reduce        1.04s    1.07s     0.943    2.68GB     2.83     5    15       5.3s <NULL> <Rprofmem [306 x 3]> <bench_tm~ <tibble ~
# 3 docall     847.69ms 863.73ms     1.15     1.79GB     1.15    10    10      8.72s <NULL> <Rprofmem [97 x 3]>  <bench_tm~ <tibble ~

(I'm really not sure how iterations= is interpreted ...)

FYI, the + in +Reduce(`|`, .SD) is analogous to your follow-up as.numeric without the extra step.

R data.table binary OR across specific columns

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