Left Join Issue in R

Question

[cthangav]

I want to merge two data frames (named 'data' and 'add') so that only the rows of the first dataframe(data) are kept (Left Join).

When I use

Merged <- merge(data, add, by.x = "DATAGene", by.y = "ADDGene", all.x = TRUE, all.y = FALSE)

I get more rows than I had in the first data frame.

dim(data)

[1] 21578 4

dim(add)

[1] 25778 2

dim(Merged)

[1] 21639 5`

Why would this happen and is there a way to avoid it?

Both the DATAGene and ADDGene columns are character columns.

The datatable "add" looks like..

ADDGene V1

1 TSPAN6 51

2 TNMD 0

3 DPM1 114

4 SCYL3 9

5 C1orf112 1

...

87 SPPL2B 6

88 FAM214B 20

89 COPZ2 75

. .

The datatable "data" looks like..

DATAGene V2 V3 V4

1 TSPAN6 294 778 595

2 TNMD 0 8 0

3 DPM1 354 311 696

4 SCYL3 86 94 134

5 C1orf112 147 268 263

...

87 FAM214B 415 115 156

88 COPZ2 82 13 12

89 PRKAR2B 1523 710 250

[Basti]

It is highly possible that one of the data.frame has duplicate value of gene name

length(unique(data$DATAGene))==nrow(data)
length(unique(add$ADDGene))==nrow(add)

[cthangav]

You are correct, the Data and Merged data tables have the same number of rows if I only count the unique ones. Do you know if there a way to keep only the rows from Data and its duplicates?

[cthangav]

I believe removing the duplicates from add using the following command fixed the issue. Thank you

add2 <- add %>% dplyr::distinct(ADDGene, .keep_all = TRUE)