Error using min() function on a list

[player1681]

Hello everybody.

I am trying to find the max and min values of the first two columns of a matrix. I have written the following code

f = open('XdataTXT.txt','r')
linesX=f.readlines()
X_column_number = 0
positionX=[]
Y_column_number = 1
positionY=[]
for x in linesX:
    positionX.append(x.split()[X_column_number])
    positionY.append(x.split()[Y_column_number])
f.close()
print(positionX)
print(max(positionX))
print(min(positionX))

However, my output does not look like what it should. The max(positionX) is returned as it should, but the min(positionX) doesn't, since the output is

Output:
-1.0000000e+00

but the smallest element is -75. Aditionally, if the same is done using the second column, positionY, the both outputs look as they should.

Can someone tell me what am I doing wrong?

Thanks.