# Merge 3 Dataframes In R

Are you a beginner (1 star), intermediate (2 stars) or advanced (3 stars) R user? Related exercise sets: Merging Dataframes Exercises Spatial Data Analysis: Introduction to Raster Processing (Part 1) Advanced Techniques With Raster Data: Part 1 – Unsupervised Classification Data Manipulation with data.table (part -2) Spatial Data Analysis. 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: merge(x, y, by, by.x, by.y, sort = TRUE).

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

By default the data frames are merged on the columns with names they both have, but separate specifications of the columns can be given by `by.x` and `by.y`. The rows in the two data frames that match on the specified columns are extracted, and joined together. If there is more than one match, all possible matches contribute one row each. For the precise meaning of ‘match’, see `match`.

Columns to merge on can be specified by name, number or by a logical vector: the name `'row.names'` or the number `0` specifies the row names. If specified by name it must correspond uniquely to a named column in the input.

### Merge 3 Dataframes In R Program

If `by` or both `by.x` and `by.y` are of length 0 (a length zero vector or `NULL`), the result, `r`, is the Cartesian 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` are appended to the result as well, with `NA` filled in the corresponding columns of `y`; analogously for `all.y`.

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

If a `by.x` column name matches one of `y`, and if `no.dups` is true (as by default), the y version gets suffixed as well, avoiding duplicate column names in the result.

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

In SQL database terminology, the default value of `all = FALSE` gives a natural join, a special case of an inner join. 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 match `NULL` records, equivalent to `incomparables = NA` in R.

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Mostly, we merge the data frames by columns because column names are considered prominent in data sets but it is also possible to merge two data frames by using rows. Merging by rows is likely to result in more uncleaned data as compared to the merging by columns. This can be done with the help of merge function and its by argument.

## Example

Consider the below data frames −

## Output

Merging df1 with df2, df1 with df3, and df2 with df3 −