Qu

drop

Builtin index · Collections & strings

result = take(xs, n)

Input: xs, n · Output: result

What it is

xs is a Vec/List; n is a number of elements.

Overloads

One call shape — this function is not overloaded.

CodeInputOutputDescription
result = take(xs, n)
xs Vec or Listxs is a Vec/List.
n numbern is a number of elements.
result —
Returns the same type as xs: the first n elements (take) or everything after them (drop). n beyond the length is clamped, not an error.

Examples

From the documentation, and run by the build -- the output and the figure below are what the engine actually produced. Simplest first.

write_csv(table(
    temp     = [21.5, 22.1, 35.0, 21.8, 36.2, 22.0, 34.5, 21.6, 35.8, 22.3],
    humidity = [45.2, 46.0, 20.1, 45.5, 19.5, 45.8, 21.0, 45.1, 20.4, 46.2],
    pressure = [1012.1, 1011.8, 1009.5, 1012.0, 1008.9, 1012.3, 1009.8, 1012.2, 1009.1, 1011.9],
    label    = ["ok", "ok", "warn", "ok", "warn", "ok", "warn", "ok", "warn", "ok"]
), "sensors.csv")

df = read_csv("sensors.csv")
print("rows = {nrow(df)}, cols = {ncol(df)}")
print(head(df, 3))

numeric = drop(df, "label")
c = corrmat(numeric)
print(c.matrix)
c.plot()
savefig("quickstart_corrmat.svg")

scaled_temp = standardize(df.temp)
print("standardized temp[0] = {scaled_temp[0]:.4f}")
print("mean(standardized) = {mean(scaled_temp):.4f}, std(standardized) = {std(scaled_temp):.4f}")
output
rows = 10, cols = 4
temp  humidity  pressure  label
----  --------  --------  -----
21.5      45.2    1012.1  ok   
22.1        46    1011.8  ok   
  35      20.1    1009.5  warn 
[1, -0.997357, -0.991317; -0.997357, 1, 0.983511; -0.991317, 0.983511, 1]
· savefig quickstart_corrmat.svg
  note: fonts render using whatever is installed on the viewer's machine (none are embedded) -- pass embed_fonts=true (fontfamily preset only) or export .tikz for guaranteed appearance
standardized temp[0] = -0.8275
mean(standardized) = -0.0000, std(standardized) = 1.0000
temp, temp: 1 1 temp, humidity: -0.997 -0.997 temp, pressure: -0.991 -0.991 humidity, temp: -0.997 -0.997 humidity, humidity: 1 1 humidity, pressure: 0.984 0.984 pressure, temp: -0.991 -0.991 pressure, humidity: 0.984 0.984 pressure, pressure: 1 1 temp humidity pressure temp humidity pressure First plot

from quickstart

How it works

data.drop("col") / data.drop(("col1", "col2")) — a new Table with the named column(s) removed (see Table::drop's own doc comment). Accepts either shape for the "which columns" argument: select's own convention of N trailing positional args (select(df, "a", "b")), or a single list value for "drop several at once" — column_names_arg below expands that one case, everything else stays identical to select's display_value-per-arg collection. The list form is a parenthesized tuple (("a", "b"), Qu's existing Value::List literal), NOT a bracketed [...] — [...] is always a numeric Vec/Mat literal here (eval_matrix_literal calls .as_num() on every cell), so ["a", "b"] with string cells already errors before reaching this builtin at all; there is no bracketed string-list literal to accept.

From the note above this builtin in the interpreter, where the reasoning was written down as it was built.

See also

take — documented in the same entry.