DataTable-class {S4Vectors} | R Documentation

## DataTable objects

### Description

DataTable is an API only (i.e. virtual class with no slots) for accessing objects with a rectangular shape like DataFrame or DelayedMatrix objects.

### Accessors

In the following code snippets, `x` is a `DataTable`.

  `nrow(x)`, `ncol(x)`: Get the number of rows and columns, respectively.

  `NROW(x)`, `NCOL(x)`: Same as `nrow(x)` and `ncol(x)`, respectively.

  `dim(x)`: Length two integer vector defined as `c(nrow(x), ncol(x))`.

  `rownames(x)`, `colnames(x)`: Get the names of the rows and columns, respectively.

  `dimnames(x)`: Length two list of character vectors defined as `list(rownames(x), colnames(x))`.

### Subsetting

In the code snippets below, `x` is a DataTable object.

  `x[i, j, drop=TRUE]`: Return a new DataTable object made of the selected rows and columns. For single column selection, the `drop` argument specifies whether or not to coerce the returned sequence to a standard vector.

  `head(x, n=6L)`: If `n` is non-negative, returns the first n rows of the DataTable object. If `n` is negative, returns all but the last `abs(n)` rows of the DataTable object.

  `tail(x, n=6L)`: If `n` is non-negative, returns the last n rows of the DataTable object. If `n` is negative, returns all but the first `abs(n)` rows of the DataTable object.

  `subset(x, subset, select, drop=FALSE)`: Return a new DataTable object using:

  subset

    logical expression indicating rows to keep, where missing values are taken as FALSE.

  select

    expression indicating columns to keep.

  drop

    passed on to `[` indexing operator.

  `na.omit(object)`: Returns a subset with incomplete cases removed.

  `na.exclude(object)`: Returns a subset with incomplete cases removed (but to be included with NAs in statistical results).

  `is.na(x)`: Returns a logical matrix indicating which cells are missing.

  `complete.cases(x)`: Returns a logical vector identifying which cases have no missing values.

### Combining

In the code snippets below, `x` is a DataTable object.

  `cbind(...)`: Creates a new `DataTable` by combining the columns of the `DataTable` objects in `...`.

  `rbind(...)`: Creates a new `DataTable` by combining the rows of the `DataTable` objects in `...`.

  `merge(x, y, ...)`: Merges two `DataTable` objects `x` and `y`, with arguments in `...` being the same as those allowed by the base `merge`. It is allowed for either `x` or `y` to be a `data.frame`.

### Looping

In the code snippets below, `x` is a DataTable object.

  `by(data, INDICES, FUN, ..., simplify = TRUE)`: Apply `FUN` to each group of `data`, a `DataTable`, formed by the factor (or list of factors) `INDICES`. Exactly the same contract as `as.data.frame`.

### Transforming

In the code snippets below, `x` is a DataTable object.

  `transform(`_data`, ...)`: adds or replaces columns based on expressions in `...`. See `transform`.

### Utilities

  `duplicated(x)`: Returns a logical vector indicating the rows that are identical to a previous row.

  `unique(x)`: Returns a new `DataTable` after removing the duplicated rows from `x`.

### Coercion

  `as.env(x, enclos = parent.frame())`: Creates an environment from `x` with a symbol for each `colnames(x)`. The values are not actually copied into the environment. Rather, they are dynamically bound using `makeActiveBinding`. This prevents unnecessary copying of the data from the external vectors into R vectors. The values are cached, so that the data is not copied every time the symbol is accessed.

  `as.data.frame(x, row.names=NULL, optional=FALSE, ...)`: Creates the corresponding data.frame.

### Statistical modeling with DataTable

A number of wrappers are implemented for performing statistical procedures, such as model fitting, with DataTable objects.

#### Tabulation

  `xtabs(formula = ~., data, subset, na.action, exclude = c(NA, NaN), drop.unused.levels = FALSE)`: Like the original `xtabs`, except `data` is a `DataTable`.

### See Also

- DataFrame for an implementation that mimics `data.frame`.

- data.frame

### Examples

    showClass("DataTable")  # shows (some of) the known subclasses

    library(IRanges)
    df <- DataFrame(as.data.frame(UCBAdmissions))
    xtabs(Freq ~ Gender + Admit, df)

[Package S4Vectors version 0.18.3 Index]