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SDcols in data.table can be tricky to remember. Here are handy examples for quick reference: 1. Use lapply with .SDcols to replace NA values with 0. 2. Aggregate data by summing specific columns using .SDcols. Keep these snippets for easy copying when needed in your data manipulation tasks.
SDcols is an useful but tricky method in data.table. The statement of it is hard to remember, so I wrote down some examples, copying and pasting when I need them.
Use lapply with .SDcols
cols <- c('COL1', 'COL2', 'COL3')
main_tb <- main_tb %>%
.[, c(cols):= lapply(.SD, function(x) ifelse(is.na(x), 0, x))
, .SDcols = cols]Aggregate with .SDcols
cols_by <- c('COL1', 'COL2')
cols_sum <- c('COL3', 'COL4')
dt <- dt %>%
.[, lapply(.SD, sum), by = item_no_col, .SDcols = cols_sum]Recommended Posts
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