How Does One Merge Dataframes by Row Name Without Adding a "Row.Names" Column

Merge data frames based on rownames in R

See ?merge:

the name "row.names" or the number 0 specifies the row names.

Example:

R> de <- merge(d, e, by=0, all=TRUE)  # merge by row names (by=0 or by="row.names")
R> de[is.na(de)] <- 0                 # replace NA values
R> de
  Row.names   a   b   c   d   e   f   g   h   i  j  k  l  m  n  o  p  q  r  s
1         1 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 11 12 13 14 15 16 17 18 19
2         2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  1  0  0  0  0  0  0  0  0  0
3         3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  0 21 22 23 24 25 26 27 28 29
   t
1 20
2  0
3 30

Merge dataframes with unequal rows, and no matching column names R

Something like this might work:

df1[df1$TreatyYear %in% df2$TreatyYear, Dates] <- df2$Earned

Example

df <- data.frame(matrix(NA,4,4))
df$X1 <- 1:4

df[df$X1 %in% c(1,2),c("X3","X4")] <- c(1,2)

merge by row.name and column

Here is one option:

merge(df1, df2, by.x = "row.names", by.y = "site")
  Row.names x y p  q
1         a 1 4 5 10
2         b 2 5 6 11

how to merge or join data frame and keep the row names as well?

I guess you want to cbind the datasets keeping the rownames. An option using data.table is

library(data.table) #data.table_1.9.5
dt <- do.call(cbind,lapply(mget(paste0("df",1:3)),
           as.data.table, keep.rownames=TRUE))
setnames(dt, seq(2,ncol(dt),by=2), rep('variable',3))
setnames(dt, seq(1,ncol(dt), by=2), paste0('row.names', 1:(ncol(dt)/2)))
head(dt,2)
#   row.names1 variable row.names2 variable row.names3 variable
#1:          1        0          1        1          1        1
#2:          2        0          2        1          2        0

Merging dataframes on row.names: column is put in capital letter

If we check the source code of merge.data.frame, it is creating the Row.names in cbind and the 0 based condition is if we specified the by for 0 i.e. for merging by row (as mentioned in the documentation part -below)

...

else {
        if (any(by.x == 0L)) {
            x <- cbind(Row.names = I(row.names(x)), x) ####
            by.x <- by.x + 1L
        }
        if (any(by.y == 0L)) {
            y <- cbind(Row.names = I(row.names(y)), y) ####
            by.y <- by.y + 1L
        }
        
...

The documentation doesn't say much about this except that

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 two data frames while keeping the original row order

Check out the join function in the plyr package. It's like merge, but it allows you to keep the row order of one of the data sets. Overall, it's more flexible than merge.

Using your example data, we would use join like this:

> join(df.2,df.1)
Joining by: class
  object class prob
1      A     2  0.7
2      B     1  0.5
3      D     2  0.7
4      F     3  0.3
5      C     1  0.5

Here are a couple of links describing fixes to the merge function for keeping the row order:

http://www.r-statistics.com/2012/01/merging-two-data-frame-objects-while-preserving-the-rows-order/

http://r.789695.n4.nabble.com/patching-merge-to-allow-the-user-to-keep-the-order-of-one-of-the-two-data-frame-objects-merged-td4296561.html

merge 2 dataframes in r with same row names

With merge, we can use the by as row.names

out <- merge(df1, df2, by = 'row.names')

---

If we need to plot, either we can use base R barplot

barplot(`row.names<-`(as.matrix(out[-1]),
          out$Row.names), col = c('blue', 'green', 'red'), legend = TRUE)

Or with tidyverse

library(ggplot2)
library(dplyr)
library(tidyr)
merge(df1, df2, by = 'row.names') %>% 
   rename(nm = 'Row.names') %>%  # // rename the column name
   type.convert(as.is = TRUE) %>%  # // some columns were not of the correct type
   pivot_longer(cols = -nm) %>% # // reshape to 'long' format
   ggplot(aes(x = name, y = value, fill = nm)) + # // plot as bar
        geom_col() + 
        theme_bw()

-output

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