Thanks, Paige, that was indeed part of the issue! I tried everything, but I indeed needed to define the x_cat as a character before the concatenate step. However, there is now the issue that it is not seeing the . as missing, but instead is doing: 42,52,118,165,206,239,247,249,267,270,272,274,276,278,278,278,281,281,289,289,289,289,289,289,289,289,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,. I thought the CATX ignored blanks. All the x variables are numerical, so I'm not sure why it's seeing these as data points. To your question about the utility of such long strings, this is a particular format of mouse-tracking data for an R package called mouse-trap that requires every X- and Y- path within a single trial to be concatenated into a single cell.
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