One error you may encounter in R is:

Error: Duplicate identifiers for rows

This error occurs when you attempt to use the spread() function to spread the values in one or more columns in a data frame into their own columns.

However, an error can occur if there is no unique ID for each row so there is no way to determine which values belong with which observations when performing the spread.

The following example shows how to fix this error in practice.

Example: How to Fix the Error

Suppose we have the following data frame in R that contains information about various basketball players:

#create data frame
df <- data.frame(player=rep(c('A', 'B'), each=4),
                 year=rep(1:4, times=2),
                 assists=c(4, 10, 4, 4, 3, 7, 7, 6),
                 points=c(14, 6, 18, 7, 22, 9, 38, 4))

#view data frame
df

  player year assists points
1      A    1       4     14
2      A    2      10      6
3      A    3       4     18
4      A    4       4      7
5      B    1       3     22
6      B    2       7      9
7      B    3       7     38
8      B    4       6      4

Now suppose we would like to transform the data frame so that we have the year column as the id column and create new columns called assists_A, assists_B, points_A, and points_B to represent the assists and points values for players A and B during each year.

Since the values in the year column will not be unique (there will be two 1’s, two 2’s, etc.) the spread()  function will produce an error.

However, we can use the pivot_wider() function with the following syntax to produce the desired data frame:

library(tidyr)

#spread the values in the points and assists columns
pivot_wider(data = df, 
            id_cols = year, 
            names_from = player, 
            values_from = c('assists', 'points'))

# A tibble: 4 x 5
   year assists_A assists_B points_A points_B
                    
1     1         4         3       14       22
2     2        10         7        6        9
3     3         4         7       18       38
4     4         4         6        7        4

Notice that we don’t receive any error and we’re able to successfully create the new columns that display the points and assists values for players A and B during each of the four years.

The following tutorials explain how to fix other common errors in R: