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For the data frame cond will be evaluated in the data.frame's context.
So columns can be referred as variables in the expression (see the examples).
If data is list then where will be applied to each element of
the list. For other types (vector/matrix) there is no non-standard
evaluation. There is a special constant .N which equals to number of
rows in data for usage in cond expression.
where(data, cond)data.frame/matrix/vector/list which contains just selected rows.
data.frame/matrix/vector/list to be subsetted
logical or numeric expression indicating elements or rows to
keep: missing values (NA) are taken as FALSE. If data is data.frame
then cond will be evaluated in the scope of the data.
# leave only 'setosa'
rows(iris, Species == "setosa")
# leave only first five rows
rows(iris, 1:5)
# example of .N usage.
set.seed(42)
train = rows(iris, sample(.N, 100))
str(train)
set.seed(42)
test = rows(iris, -sample(.N, 100))
str(test)
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