[datatable-help] Row wise operation in data.table

[Serdar Akin]

Hi,

Currently I'm trying to find a way to make row wise operation within
data.table to find value that have
a certain pattern, and to count those.

For instance find the number of 3 for each Respid and count those for each
row.
set.seed(1)
DT    <- data.table( Respid = seq(1,100, 1),
                    Q1 = rep(1:5, each = 20),
                    Q2 = as.integer(runif(100, min = 1, max = 5) ),
                    Q3   = sample(1:5, 100, replace = T)
)

DT1    <- DT[, lapply(.SD, function(x) length(grep(3, x))), by = 'Respid']

A do get 1 for each column that has a 3 in it but no column that counts it.

Regards Serdar
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