{Solved} Error In Fix.by(by.y, y): ‘by’ Must Specify A Uniquely Valid Column

If you try to merge two data frames by a column that is only present in one of the data frames, the error fix will be raised. y = by(by.y): ‘by’ must specify a column that is unique.

You can avoid this error by using a column name that appears in both data frames for the by parameter, or by using the unique column names in by.x and by.y.

What Is Merge in R?

The merge function joins two data frames that have a similar column or row names. If you want to merge data frames in R, you must include a column name in the by parameter.

You can use by if the column names are the same. If the column names are different for each data frame, you must specify by.x and by.y.

Solution To This Error

This error can be solved using by.x and by.y. The parameter by.x must have a column name that is unique to the first data frame, and the parameter by.y must have a column name that is unique to the second. Let’s take a look at the updated code:

dat_merge <- merge(dat1, dat2, by.x=’var_ID’, by.y=’VAR_ids’)


Let us check the result:

   var_ID         x1         y1
1       1 -0.4343253 -0.8518977
2       2 -0.5291911  0.0305206
3       3  1.2316967  0.4972952
4       4 -0.4829048  2.1803895
5       5  0.2598425 -2.6383560
6       6 -0.7514874 -1.2931126
7       7 -0.6536955  0.7551982
8       8 -0.8750813 -0.1333365
9       9 -0.2649102 -0.3959812
10     10  0.3956067  1.2125677

As we can see, we have successfully merged the two frames.

Also read:- [Fixed] Error Code: WUC- 1002 Spectrum Error In 4 Easy Steps


Programming errors are common, by correcting errors we improve our skills. If you made this error then that’s completely fine, just going through this article will allow you to fix those errors and improve your skills. So get programming!

And please share this article with any of your friends that require assistance in solving this error.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top