select_replace_vars: Fast Select, Replace or Add Data Frame Columns

In collapse: Advanced and Fast Data Transformation

Fast Select, Replace or Add Data Frame Columns

Description

Efficiently select and replace (or add) a subset of columns from (to) a data frame. This can be done by data type, or using expressions, column names, indices, logical vectors, selector functions or regular expressions matching column names.

Usage

## Select and replace variables, analgous to dplyr::select but significantly faster
fselect(.x, ..., return = "data")
fselect(x, ...) <- value
slt(.x, ..., return = "data")   # Shorthand for fselect
slt(x, ...) <- value            # Shorthand for fselect<-

## Select and replace columns by names, indices, logical vectors,
## regular expressions or using functions to identify columns

get_vars(x, vars, return = "data", regex = FALSE, rename = FALSE, ...)
      gv(x, vars, return = "data", ...)   # Shorthand for get_vars
     gvr(x, vars, return = "data", ...)   # Shorthand for get_vars(..., regex = TRUE)

get_vars(x, vars, regex = FALSE, ...) <- value
      gv(x, vars, ...) <- value           # Shorthand for get_vars<-
     gvr(x, vars, ...) <- value           # Shorthand for get_vars<-(..., regex = TRUE)

## Add columns at any position within a data.frame

add_vars(x, ..., pos = "end")
add_vars(x, pos = "end") <- value
      av(x, ..., pos = "end")             # Shorthand for add_vars
      av(x, pos = "end") <- value         # Shorthand for add_vars<-

## Select and replace columns by data type

num_vars(x, return = "data")
num_vars(x) <- value
      nv(x, return = "data")       # Shorthand for num_vars
      nv(x) <- value               # Shorthand for num_vars<-
cat_vars(x, return = "data")       # Categorical variables, see is_categorical
cat_vars(x) <- value
char_vars(x, return = "data")
char_vars(x) <- value
fact_vars(x, return = "data")
fact_vars(x) <- value
logi_vars(x, return = "data")
logi_vars(x) <- value
date_vars(x, return = "data")      # See is_date
date_vars(x) <- value

Arguments

x, .x	a data frame or list.
value	a data frame or list of columns whose dimensions exactly match those of the extracted subset of x. If only 1 variable is in the subset of x, value can also be an atomic vector or matrix, provided that NROW(value) == nrow(x).
vars	a vector of column names, indices (can be negative), a suitable logical vector, or a vector of regular expressions matching column names (if regex = TRUE). It is also possible to pass a function returning TRUE or FALSE when applied to the columns of x.
return	an integer or string specifying what the selector function should return. The options are: Int. String Description 1 "data" subset of data frame (default) 2 "names" column names 3 "indices" column indices 4 "named_indices" named column indices 5 "logical" logical selection vector 6 "named_logical" named logical vector Note: replacement functions only replace data, however column names are replaced together with the data (if available).
regex	logical. TRUE will do regular expression search on the column names of x using a (vector of) regular expression(s) passed to vars. Matching is done using grep.
rename	logical. If vars is a named vector of column names or indices, rename = TRUE will use the (non missing) names to rename columns.
pos	the position where columns are added in the data frame. "end" (default) will append the data frame at the end (right) side. "front" will add columns in front (left). Alternatively one can pass a vector of positions (matching length(value) if value is a list). In that case the other columns will be shifted around the new ones while maintaining their order.
...	for fselect: column names and expressions e.g. fselect(mtcars, newname = mpg, hp, carb:vs). for get_vars: further arguments passed to grep, if regex = TRUE. For add_vars: multiple lists/data frames or vectors (which should be given names e.g. name = vector). A single argument passed may also be an (unnamed) vector or matrix.

Details

get_vars(<-) is around 2x faster than `[.data.frame` and 8x faster than `[<-.data.frame`, so the common operation data[cols] <- someFUN(data[cols]) can be made 10x more efficient (abstracting from computations performed by someFUN) using get_vars(data, cols) <- someFUN(get_vars(data, cols)) or the shorthand gv(data, cols) <- someFUN(gv(data, cols)).

Similarly type-wise operations like data[sapply(data, is.numeric)] or data[sapply(data, is.numeric)] <- value are facilitated and more efficient using num_vars(data) and num_vars(data) <- value or the shortcuts nv and nv<- etc.

fselect provides an efficient alternative to dplyr::select, allowing the selection of variables based on expressions evaluated within the data frame, see Examples. It is about 100x faster than dplyr::select but also more simple as it does not provide special methods (except for 'sf' and 'data.table' which are handled internally) .

Finally, add_vars(data1, data2, data3, ...) is a lot faster than cbind(data1, data2, data3, ...), and preserves the attributes of data1 (i.e. it is like adding columns to data1). The replacement function add_vars(data) <- someFUN(get_vars(data, cols)) efficiently appends data with computed columns. The pos argument allows adding columns at positions other than the end (right) of the data frame, see Examples. Note that add_vars does not check duplicated column names or NULL columns, and does not evaluate expressions in a data environment, or replicate length 1 inputs like cbind. All of this is provided by ftransform.

All functions introduced here perform their operations class-independent. They all basically work like this: (1) save the attributes of x, (2) unclass x, (3) subset, replace or append x as a list, (4) modify the "names" component of the attributes of x accordingly and (5) efficiently attach the attributes again to the result from step (3). Thus they can freely be applied to data.table's, grouped tibbles, panel data frames and other classes and will return an object of exactly the same class and the same attributes.

Note

In many cases functions here only check the length of the first column, which is one of the reasons why they are so fast. When lists of unequal-length columns are offered as replacements this yields a malformed data frame (which will also print a warning in the console i.e. you will notice that).

See Also

fsubset, ftransform, rowbind, Data Frame Manipulation, Collapse Overview

Examples

## Wold Development Data
head(fselect(wlddev, Country = country, Year = year, ODA)) # Fast dplyr-like selecting
head(fselect(wlddev, -country, -year, -PCGDP))
head(fselect(wlddev, country, year, PCGDP:ODA))
head(fselect(wlddev, -(PCGDP:ODA)))
fselect(wlddev, country, year, PCGDP:ODA) <- NULL          # Efficient deleting
head(wlddev)
rm(wlddev)

head(num_vars(wlddev))                                     # Select numeric variables
head(cat_vars(wlddev))                                     # Select categorical (non-numeric) vars
head(get_vars(wlddev, is_categorical))                     # Same thing

num_vars(wlddev) <- num_vars(wlddev)                       # Replace Numeric Variables by themselves
get_vars(wlddev,is.numeric) <- get_vars(wlddev,is.numeric) # Same thing

head(get_vars(wlddev, 9:12))                               # Select columns 9 through 12, 2x faster
head(get_vars(wlddev, -(9:12)))                            # All except columns 9 through 12
head(get_vars(wlddev, c("PCGDP","LIFEEX","GINI","ODA")))   # Select using column names
head(get_vars(wlddev, "[[:upper:]]", regex = TRUE))        # Same thing: match upper-case var. names
head(gvr(wlddev, "[[:upper:]]"))                           # Same thing

get_vars(wlddev, 9:12) <- get_vars(wlddev, 9:12)           # 9x faster wlddev[9:12] <- wlddev[9:12]
add_vars(wlddev) <- STD(gv(wlddev,9:12), wlddev$iso3c)     # Add Standardized columns 9 through 12
head(wlddev)                                               # gv and av are shortcuts

get_vars(wlddev, 14:17) <- NULL                            # Efficient Deleting added columns again
av(wlddev, "front") <- STD(gv(wlddev,9:12), wlddev$iso3c)  # Again adding in Front
head(wlddev)
get_vars(wlddev, 1:4) <- NULL                              # Deleting
av(wlddev,c(10,12,14,16)) <- W(wlddev,~iso3c, cols = 9:12, # Adding next to original variables
                               keep.by = FALSE)
head(wlddev)
get_vars(wlddev, c(10,12,14,16)) <- NULL                   # Deleting

head(add_vars(wlddev, new = STD(wlddev$PCGDP)))                  # Can also add columns like this
head(add_vars(wlddev, STD(nv(wlddev)), new = W(wlddev$PCGDP)))   # etc...

head(add_vars(mtcars, mtcars, mpg = mtcars$mpg, mtcars), 2)      # add_vars does not check names!

collapse documentation built on Nov. 3, 2024, 9:08 a.m.