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Asked: 2026-05-30T08:22:41+00:00

I am using a subset to extract from set of a column values I

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I am using a subset to extract from set of a column values

I have a DF with several columns, one of them is state. I need to get frequencies for state but just for some set of states. So I have this:

tmp <- subset(DF, DF$STATE %in% SOMESTATES)
a   <- as.data.frame(table(tmp$STATE))

This is almost fine. The tmp data frame has only the records belonging to the SOMESTATES set, fine.

The issue is a. The table result is the complete frequencies for the whole DF, not the tmp only. The other has zero values.

My problem here is some states in SOMESTATES has zero appearances in the DF, which this prevents me to use droplevels. droplevels takes out also those zero values. Here as well:

If I use droplevels like this, for example, I loose the zero values for some states that I need.

tmp <- subset(DF, DF$STATE %in% SOMESTATES)
tmp2 <- droplevels(tmp)
table(tmp2$STATE)

presents all the states not only the ones in SOMESTATES

Any advise is appreciated

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1 Answer

  1. Editorial Team

    Try something like:

    tmp <- subset(DF, DF$STATE %in% SOMESTATES) 
tmp$STATE <- factor(tmp$STATE, levels=SOMESTATES) 
table(tmp$STATE)

    The factor function will recreate it into a new factor whose levels match SOMESTATES exactly. Those states who are not in SOMESTATES will not be included as they are neither in the data nor SOMESTATES, but those states with 0 count that are in SOMESTATES will still be included in the factor, and hence the table with 0 counts.

    Note also that the factor levels will be ordered by SOMESTATES so the order in that vector will be the order that shows up in the tables or plots using it. Generally this is benign or useful.

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