dplyr operation that I don't know

selection

• X:Y (column X to Y)
• start_with (string)
• end_with (string)
• matches (regex)
• contains (string)

conditons

• if_else(condition, TRUE_operation, FASLE_operation)

• case_when(condition ~ operation_if_TRUE)

across and c_aross

across is a verb for selected column （i.e., vector) c_across is a verb for row, but must be used with rowwise()

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# calculate mean for x and y column vector,  imagine x=mean(x), y=mean(y)
df %>% mutate(across(c(x,y), mean))

## Yes, it can't be used in the same functional programming way, how weird!
df %>% rowwise() %>% mutate(m = mean(c_across(c(x,y))))

lambda function (in purrr package)

~ = lambda, .x = argument

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## plus 1 for selected column vector, imagine x=x+1, y=y+1
df %>% mutate(across(c(x,y), ~ .x + 1))

to be continue …