Incrementing data.table value based on another data.table value

1
votes

I have two data.tables, and one has a subset of rows/columns of another. I'd like to increment values of the larger data.table by 1 for every non-zero value in smaller table:

DT1 <- as.data.table(matrix(c(0, 1, 2, 3), nrow=2, ncol=2, 
       dimnames=list(c("a", "b"), c("a", "b"))), keep=T)
DT2 <- as.data.table(matrix(c(0, 0, 1, 2, 2, 1, 1, 0, 3), nrow=3, ncol=3, 
       dimnames=list(c("a", "b", "c"), c("a", "b", "c"))), keep=T)

DT1
#   rn a b
#1:  a 0 2
#2:  b 1 3
DT2
#   rn a b c
#1:  a 0 2 1
#2:  b 0 2 0
#3:  c 1 1 3

I'd like to increment values in DT2 so that I get

#   rn a b c
#1:  a 0 3 1
#2:  b 1 3 0
#3:  c 1 1 3

(This is similar to my previous question on adding DT1 and DT2: Adding values in two data.tables... I need to do both :) )

2
rdata.table

2 Answers

5
votes

Another way:

require(data.table) # v1.9.6+
xcols = c("a", "b")
icols = paste0("i.", xcols) # "i.*" to refer to DT1's cols
DT2[DT1, (xcols) := Map(function(x, y) x + (y > 0L), mget(xcols), mget(icols)), on="rn"]

How this should look like:

DT2[DT1, (xcols) := Map(function(x, y) x + (y > 0L), .SD, i.SD), .SDcols=xcols, i.SDcols = icols]

or even better would be:

DT2[DT1, (xcols) := .SD + (i.SD > 0L), .SDcols=xcols, i.SDcols=icols]
2
votes

I'd consider something like...

inc_em <- with(melt(DT1)[value != 0], split(rn, variable))

for (k in names(inc_em))
    DT2[.(rn = inc_em[[k]]), (k) := get(k) + 1, on="rn" ]

#    rn a b c
# 1:  a 0 3 1
# 2:  b 1 3 0
# 3:  c 1 1 3