1

Here's a simplified example. I've got a data frame

data <- structure(list(day = structure(c(1L, 2L, 3L, 1L, 2L, 3L, 4L, 
4L), levels = c("6", "10", "13", "26"), class = "factor"), measurement = c(114.243333333333, 
114.473333333333, 115.276666666667, 114.243333333333, 114.51, 
115.3, 115.476666666667, 115.56)), class = "data.frame", row.names = c(NA, 
-8L))

When I try and plot with ggstatsplot

library(ggstatsplot)
ggbetweenstats(data = data,
              x = day, y = measurement)

I get this error:

Error in data.frame(..., check.names = FALSE) : 
  arguments imply differing number of rows: 0, 1

But they are the same length!

> length(data$day)
[1] 8
> length(data$measurement)
[1] 8

What's going on??

Mike
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1 Answers1

2

Using the debugger, we can track the problem down to pairwise_comparisons, which is what throws the error:

pairwise_comparisons(data, day, measurement)
#> Error in data.frame(..., check.names = FALSE) : 
#>   arguments imply differing number of rows: 0, 1

And by debugging this function, we find that the error is thrown here:

df <- suppressWarnings(exec(.fn = .f, x = y_vec, g = x_vec, groups = x_vec, 
    blocks = g_vec, paired = paired, p.adjust.method = "none", 
    !!!.f.args)) %>% tidy_model_parameters(.) %>% rename(group2 = group1, 
    group1 = group2)

From examining these variables, we find that .f is PMCMRplus::gamesHowellTest, which although it does not throw an error, certainly doesn't like the input:

PMCMRplus::gamesHowellTest(data$measurement, g = data$day)

    Pairwise comparisons using Games-Howell test

data: data$measurement and data$day

   6 10 13
10 - -  - 
13 - -  - 
26 - -  -

Essentially, it cannot carry out pairwise comparisons because there are not enough observations (only 2 in each group, which is insufficient to generate p values). Therefore when this result is passed to tidy_model_parameters(.), and the code tries to create a summary data frame including p values, the p value column is missing.

Ultimately it is therefore cbind that throws the error when the function attempts to bind a length-0 column to a length-1 column. We can replicate this exact error by trying to cbind a 1-row and 0-row data frame together:

cbind(data.frame(a = 1), data.frame(b = numeric()))
#> Error in data.frame(..., check.names = FALSE) : 
#>   arguments imply differing number of rows: 1, 0

So it is not your data frame, but the summary data frame of pairwise comparisons that has different row numbers. The obvious solution is to not attempt pairwise comparisons with such a small number of observations:

ggbetweenstats(data = df,
               x = day, 
               y = measurement, 
               pairwise.comparisons = FALSE)

enter image description here

Note also that if we give it enough data points (even just by binding two copies of your data frame together), we get a pairwise comparison plot without any errors:

ggbetweenstats(data = rbind(df, df),
               x = day, 
               y = measurement)

enter image description here

To be fair, this error is essentially uncaught by ggstatsplot, since there is no specific message to tell you what caused it or why, and it takes a bit of digging to discover the problem. Might be worth filing a bug report on the ggstatplot github page?

Allan Cameron
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