Separate a collection of error codes practice in uipath foundation training

Hi, i am new to uipath space and i was trying to solve one of the practice questions on SWITCH, the practice question is "**Considering a collection of error codes stored in an Array of Strings, separate them based on their type of error code (“Ax”, “Bx” or “Cx”) and store them in 3 different arrays

The initial Array should contain the following values:

in this once i add an array with default error codes and then a For each loop to read each item in the array the solution says to add the switch activity with expression “item.Substring(0,2).ToLower” why do we need to change the case to Lower case?
also what does this expression mean axArray.Concat({item}).ToArray

Hey @Shammy_Isaac_Varghese

Item.substring.tolower- since the error codes could be in any case so we need to bring them in one format to use it in particular case in switch.

Array.concat.toarray- used to add items in the array.