matchColumn: Match a column in data.frame to a master vector

Description

Given a vector known as master vcector, a data.frame and one column of the data.frame, the function matchColumnIndex matches the values in the column to the master vector, and returns the indices of each value in the column with respect to the vector. The function matchColumn returns whole or subset of the data.frame, with the matching column in the exact order of the vector.

Usage

matchColumn(vector, data.frame, column, multi = FALSE)

Arguments

vector

A vector, probably of character strings.

data.frame

A data.frame object

column

The column name (character) or index (integer between 1 and the column number), indicating the column to be matched. Exceptionally 0 is as well accepted, which will match the row names of the data.frame to the given vector.

multi

Logical, deciding what to do if a value in the vector is matched to several values in the data.frame column. If set to TRUE, all rows containing the matched value in the specified column are returned; otherwise, when the value is set to FALSE, one arbitrary row is returned. See details and examples below.

Value

For matchColumnIndex, if multi is set to FALSE, an integer vector of the same length as the master vector, indicating the order of the data.frame rows by which the column can be re-organized into the master vector. When multi is TRUE, the returning object is a list of the same length as the master vector, each item containing the index (indices) of data.frame rows which match to the master vector.

For matchColumn, a data.frame is always returned. In case multi=FALSE, the returning data frame has the same number of rows as the length of the input master vector, and the column which was specified to match contains the master vector in its order. If multi=TRUE, returned data frame can contain equal or more numbers of rows than the master vector, and multiple-matched items are repeated.

Details

See more details below.

The function is used to address the following question: how can one order a data.frame by values of one of its columns, the order for which is given in a vector (known as “master vector”). matchColumnIndex and matchColumn provide thoroughly-tested implementation to address this question.

For one-to-one cases, where both the column and the vector have no duplicates and can be matched one-to-one, the question is straightforward to solve with the match function in R. In one-to-many or many-to-many matching cases, the parameter multi determines whether multiple rows matching the same value should be shown. If mutli=FALSE, then the sorted data.frame that are returned has exactly the same row number as the input vector; otherwise, the returned data.frame has more rows. See the examples below.

In either case, in the returned data.frame object by matchColumn, values in the column used for matching are overwritten by the master vector.If multi=TRUE, the order of values in the column is also obeying the order of the master vector, with exceptions of repeating values casued by mutliple matching.

The column parameter can be either character string or non-negative integers. In the exceptional case, where column=0L (“L” indicates integer), the row names of the data.frame is used for matching instead of any of the columns.

Both functions are NA-friendly, since NAs in neither vector nor column should break the code.

Examples

Run this code

# NOT RUN {
df <- data.frame(Team=c("HSV", "BVB", "HSC", "FCB", "HSV"),
                 Pkt=c(25,23,12,18,21),
                 row.names=c("C", "B", "A", "F", "E"))
teams <- c("HSV", "BVB", "BRE", NA)
ind <- c("C", "A", "G", "F", "C", "B", "B", NA)

matchColumnIndex(teams, df, 1L, multi=FALSE)
matchColumnIndex(teams, df, 1L, multi=TRUE)
matchColumnIndex(teams, df, "Team", multi=FALSE)
matchColumnIndex(teams, df, "Team", multi=TRUE)
matchColumnIndex(teams, df, 0, multi=FALSE)
matchColumnIndex(ind, df, 0, multi=FALSE)
matchColumnIndex(ind, df, 0, multi=TRUE)

matchColumn(teams, df, 1L, multi=FALSE)
matchColumn(teams, df, 1L, multi=TRUE)
matchColumn(teams, df, "Team", multi=FALSE)
matchColumn(teams, df, "Team", multi=TRUE)
matchColumn(ind, df, 0, multi=FALSE)
matchColumn(ind, df, 0, multi=TRUE)

# }