dua string dalam satu string r
> toString(ddf$year)
[1] "1983, 1983, 1983, 1983"
>
> toString(ddf$period)
[1] "M01, M02, M03, M04"
>
> paste(toString(ddf$year), toString(ddf$period))
[1] "1983, 1983, 1983, 1983 M01, M02, M03, M04"
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