# Error_message: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

I'm having a problem with my code: when I make a search in the i-th column of the matrix it gives me the following error:

``````if grades[:,i]!=-3:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
``````

I have tried to read the older posts on this issue, but can't really relate to my problem

I am trying to program a grading function according to danish grading-scale

``````def computeFinalGrades(grades):
#looping over the leth of grades
for i in range(len(loopingrange)):
#checking if any grade in the i-th coloumn is -3
if grades[:,i]==-3:
#if a grade is equal to -3 then the output variabel gradesFinal is -3
gradesFinal = -3
else:
#looping over all grade coloumns that do not contain one or more grades of -3
for i in range(len(loopingrange)):
#Checking to see if any coloumn only contains 1 grade
if (len(grades[:,i]) == 1):
# if a coloumn only contains 1 grade - that is also the final grade
gradesFinal = grades[:,i]
#Checking to see if coloumn contains more than 1 grade and those grades are not -3
elif (len(grades[:,i]) > 1):
#storing all the grades in a variabel - in random order
unsortedgrades = grades[:,i]
#sorting all the grades from lowest to highest
sortedgrades1 = np.sort(unsortedgrades)
#slicing the lowest grade out using indexing
sortedgrades = sortedgrades1[1::]
#finding the final grade as the mean of the n-1 grades
gradesFinal = np.mean(sortedgrades)
return gradesFinal
``````

## 1 answer

• answered 2018-04-14 15:46

`grades[:,i]` returns the ith column of the array. This means that it is an array with one element for each row.

You cannot use `if grades[:,i]==-3:` because `grades[:,i]==-3` returns a boolean array, which cannot be used in an if statement.

If you want to check if any grade in that column == -3, you can use `-3 in grades[:,i]`.