Python Forum

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.

Well the thing is that you probably want to do the max and min over a list of number right?
what you are building there are list of strings. For the max function it will work kind of since in comparison of strings a 7 is still greater than a 5 (alphabetically). For the min function the 1 (of -1.0000000e+00) is less than the 7 (of -75) therefore it is the minimum. So the script works right, but not like you want it to. try converting the strings you get out of the file to float:

for x in linesX:
    positionX.append(float(x.split()[X_column_number]))
    positionY.append(float(x.split()[Y_column_number]))

Be careful though if you got an empty string from somewhere (it can happen) you get a problem converting

(Jan-29-2020, 04:18 PM)ThiefOfTime Wrote: [ -> ]Well the thing is that you probably want to do the max and min over a list of number right?
what you are building there are list of strings. For the max function it will work kind of since in comparison of strings a 7 is still greater than a 5 (alphabetically). For the min function the 1 (of -1.0000000e+00) is less than the 7 (of -75) therefore it is the minimum. So the script works right, but not like you want it to. try converting the strings you get out of the file to float:

for x in linesX:
    positionX.append(float(x.split()[X_column_number]))
    positionY.append(float(x.split()[Y_column_number]))

Be careful though if you got an empty string from somewhere (it can happen) you get a problem converting

Yes that was exactly the problem. Thanks.