R Merge Two Dataframes

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Example 1: Combine Data by Two ID Columns Using merge Function In Example 1, I’ll illustrate how to apply the merge function to combine data frames based on multiple ID columns. For this, we have to specify the by argument of the merge function to be equal to a vector of ID column names (i.e. By = c (“ID1”, “ID2”)).

  • By default the data frames are merged on the columns with names they both have, but separate specifcations of the columns can be given by by.xand by.y. Columns can be specified by name, number or by a logical vector: the name 'row.names'or the number.
  • To merge two data frames (datasets) horizontally, use the merge function. In most cases, you join two data frames by one or more common key variables (i.e., an inner join). # merge two data frames by ID total merge(data frameA,data frameB,by='ID') # merge two data frames by ID and Country total merge(data frameA,data frameB,by=c('ID','Country')) Adding Rows.

Abbreviation: mrg A horizontal merge combines data frames horizontally, that is, adds variables (columns) to an existing data frame, such as with a common shared ID field. Performs the horizontal merge based directly on the standard R merge function. The vertical merge is based on the rbind function in which the two data frames have the same variables but different cases (rows), so the rows. The second data frame also contains five rows and four columns, including the two ID columns ID1 and ID2. Example 1: Combine Data by Two ID Columns Using merge Function. In Example 1, I’ll illustrate how to apply the merge function to combine data frames based on multiple ID columns. For this, we have to specify the by argument of the merge function to be equal to a vector of ID column names (i.e. By = c(“ID1”, “ID2”)).

Two
merge {base}R Documentation

Merge Two Data Frames

Description

Merge two data frames by common columns or row names, or do otherversions of database join operations.

Usage

Arguments

x, y

data frames, or objects to be coerced to one.

by, by.x, by.y

specifications of the columns used for merging.See ‘Details’.

all

logical; all = L is shorthand for all.x = L andall.y = L, where L is either TRUE orFALSE.

all.x

logical; if TRUE, then extra rows will be added tothe output, one for each row in x that has no matching row iny. These rows will have NAs in those columns that areusually filled with values from y. The default isFALSE, so that only rows with data from both x andy are included in the output.

all.y

logical; analogous to all.x.

sort

logical. Should the result be sorted on the bycolumns?

suffixes

a character vector of length 2 specifying the suffixesto be used for making unique the names of columns in the resultwhich are not used for merging (appearing in by etc).

no.dups

logical indicating that suffixes are appended inmore cases to avoid duplicated column names in the result. Thiswas implicitly false before R version 3.5.0.

incomparables

values which cannot be matched. Seematch. This is intended to be used for merging on onecolumn, so these are incomparable values of that column.

...

arguments to be passed to or from methods.

Details

merge is a generic function whose principal method is for dataframes: the default method coerces its arguments to data frames andcalls the 'data.frame' method.

By default the data frames are merged on the columns with names theyboth have, but separate specifications of the columns can be given byby.x and by.y. The rows in the two data frames thatmatch on the specified columns are extracted, and joined together. Ifthere is more than one match, all possible matches contribute one roweach. For the precise meaning of ‘match’, seematch.

Columns to merge on can be specified by name, number or by a logicalvector: the name 'row.names' or the number 0 specifiesthe row names. If specified by name it must correspond uniquely to anamed column in the input.

R merge two dataframes with different columns

If by or both by.x and by.y are of length 0 (alength zero vector or NULL), the result, r, is theCartesian product of x and y, i.e.,dim(r) = c(nrow(x)*nrow(y), ncol(x) + ncol(y)).

If all.x is true, all the non matching cases of x areappended to the result as well, with NA filled in thecorresponding columns of y; analogously for all.y.

R Join Two Dataframe

If the columns in the data frames not used in merging have any commonnames, these have suffixes ('.x' and '.y' bydefault) appended to try to make the names of the result unique. Ifthis is not possible, an error is thrown.

If a by.x column name matches one of y, and ifno.dups is true (as by default), the y version gets suffixed aswell, avoiding duplicate column names in the result.

The complexity of the algorithm used is proportional to the length ofthe answer.

In SQL database terminology, the default value of all = FALSEgives a natural join, a special case of an innerjoin. Specifying all.x = TRUE gives a left (outer)join, all.y = TRUE a right (outer) join, and both(all = TRUE) a (full) outer join. DBMSes do not matchNULL records, equivalent to incomparables = NA in R.

Value

A data frame. The rows are by default lexicographically sorted on thecommon columns, but for sort = FALSE are in an unspecified order.The columns are the common columns followed by theremaining columns in x and then those in y. If thematching involved row names, an extra character column calledRow.names is added at the left, and in all cases the result has‘automatic’ row names.

Note

This is intended to work with data frames with vector-like columns:some aspects work with data frames containing matrices, but not all.

R Merge Two Dataframes

Currently long vectors are not accepted for inputs, which are thusrestricted to less than 2^31 rows. That restriction also applies tothe result for 32-bit platforms.

See Also

data.frame,by,cbind.

dendrogram for a class which has a merge method.

Examples

Combine Data Frames in R

In this tutorial, we will learn how to merge or combine two data frames in R programming.

Two R data frames can be combined with respect to columns or rows. We will look into both of these ways.

  • To combine data frames based on a common column(s), i.e., adding columns of second data frame to the first data frame with respect to a common column(s), you can use merge() function.
  • To combine data frames: with rows of second data frame added to those of the first one, you can use rbind() function.

R Combine Data Frames – Merge based on a common column(s)

merge() function is used to merge data frames. The syntax of merge() function is:

R Merge Two Dataframes

where

  • x, y are data frames, or objects to be coerced or combined to one
  • by, by.x, by.y are specifcations of the common columns.
  • sort logical (TRUE or FALSE). Results are sorted on the by columns if TRUE and not if FALSE.

Example 1 – Combine Data Frames in R using merge()

In this example, we take two data frames. The first data frame contains id and name of students. The second data frame contains id and marks of students.

You can combine these two data frames with respect to the common column id using merge() function.

Merge

The second data frame is added to the first data frame based on a column. The result is a new data frame with new columns.

This is useful when you collect the experimental data from different sources pertaining to the same experiments. Data from a source contains data collected for certain features while other source collects data for other features. Now, using merge(), you can combine these data to get a single data frame containing all the features values of experiments.

R Combine Data Frames – Concatenate Rows of Data Frame to another Data Frame

rbind() function is used to concatenate data frames. The syntax of rbind() function is:

where

  • x an R6Frame
  • ... additional parameters sent to rbind

R Merge Multiple Data Frames

Example 2 – Combine Data Frames in R using rbind()

In this example, we take two data frames. The first data frame contains id and name of students. The second data frame also contains id and name of students. Consider that these are two batches of students and we would like to concatenate these.

R Merge Two Dataframes

You can combine these two data frames with respect to rows using rbind() function.

Merge Two Dataframes In R

The rows of second data frame are added to that of first data frame. The result is a new data frame with increased number of rows.

Conclusion

R Merge Two Data Frames By Column Names

In this R Tutorial, we have learned how to combine R Data Frames based on rows or columns.