· Data manipulation, GNU-R

The following text from the R help pages clearly explains the use of command subset in extracting data from a data.frame. This command will be of much use in preparation of data set for further analysis.



subset {base} R Documentation

Subsetting Vectors and Data Frames


Return subsets of vectors or data frames which meet conditions.

subset(x, …)

## Default S3 method:
subset(x, subset, …)

## S3 method for class ‘data.frame’:
subset(x, subset, select, drop = FALSE, …)

x object to be subsetted.
subset logical expression.
select expression, indicating columns to select from a data frame.
drop passed on to [ indexing operator.
… further arguments to be passed to or from other methods.

For ordinary vectors, the result is simply x[subset & !].

For data frames, the subset argument works similarly on the rows. Note that subset will be evaluated in the data frame, so columns can be referred to (by name) as variables.

The select argument exists only for the method for data frames. It works by first replacing names in the selection expression with the corresponding column numbers in the data frame and then using the resulting integer vector to index the columns. This allows the use of the standard indexing conventions so that for example ranges of columns can be specified easily.

The drop argument is passed on to the indexing method for data frames.

An object similar to x contain just the selected elements (for a vector), rows and columns (for a data frame), and so on.

Peter Dalgaard
See Also

[, transform

subset(airquality, Temp > 80, select = c(Ozone, Temp))
subset(airquality, Day == 1, select = -Temp)
subset(airquality, select = Ozone:Wind)

with(airquality, subset(Ozone, Temp > 80))

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