c# - When i iterate through count, my array changes size, why? -

when run simple code designed make training , testing data cross-validate, iterate through each count of list each time iterates list decreases 1.

for (var = 0; < adjusteddata.count; i++)         {             var tempdata = adjusteddata;             var testdata = tempdata[i].toarray();             var traindatalist = tempdata;             traindatalist.removeat(i);             var traindata = traindatalist.toarray(); 

you're removing element of array when call traindatalist.removeat(i);. not same clearing value: traindatalist[i] = null;;

let's use real-world example. imagine array series of cups lined on table. when call traindatalist.removeat(i);, you're removing 1 of cups. when call traindatalist[i] = null;, you're leaving cup there dumping out contents.