How do I match values?-CodePudding

I've got a problem where I want to place values in an array at certain matching values.

I've got displacement_gsj_values filled with values I want to transplant, displacement_gsj_match filled with the corresponding value match (in order) and displacement_all a bigger array filled with corresponding matches of displacement_gsj.

Example:

displacement_gsj_values = [[-3.4],[0],[3.874],[7.4],[0.55],[-0.98],[0],[9.99],[-0.35]]

displacement_gsj_match  = [[3],[4],[5],[9],[10],[11],[15],[16],[17]]

displacement_all = [[0],[0],[0],[3],[4],[5],[0],[0],[0],[9],[10],[11],[0],[0],[0],[9],[15],[11],[16],[4],[5],[9],[17],[11]]

I thought about a loop that should do this:

for i in displacement_all:
    if i != 0:
        if i in displacement_all[i] == displacement_gsj_match["any value of displacement_gsj_match with the same value of i"]:
            displacement_all[i] = displacement_gsj_values["the index of the above matched value"]
    
    else:
        pass

It should place the values of displacement_gsj_values with the corresponding index out of displacement_gsj_match (both in order) into displacement_all at the matching value. The result should look like this:

displacement_all = [[0],[0],[0],[-3.4],[0],[3.874],[0],[0],[0],[7.4],[0.55],[-0.98],[0],[0],[0],[7.4],[0],[-0.98],[9.99],[0],[3.874],[7.4],[-0.35],[-0.98]]

Had to post it again because someone just answered and then deleted his answer.

CodePudding user response：

I would first of all create a dictionary that maps values to their replacement:

# Flatten the list of lists
displacement_gsj_match = sum(displacement_gsj_match, [])
displacement_gsj_values = sum(displacement_gsj_values, [])

# Create dictionary with match as key and replacement as value
replacements = dict(zip(displacement_gsj_match, displacement_gsj_values))

Looks like this and makes substitution easier:

{3: -3.4,
 4: 0,
 5: 3.874,
 9: 7.4,
 10: 0.55,
 11: -0.98,
 15: 0,
 16: 9.99,
 17: -0.35}

Then you go over your list and check if the value can be replaced or stays the same. I used the get() function, where the second argument is the default value. This means if the value is in the dictionary you replace it otherwise default to the existing value:

new_displacement = [[replacements.get(x[0], x[0])] for x in displacement_all]

Output:

[[0],
 [0],
 [0],
 [-3.4],
 [0],
 [3.874],
 [0],
 [0],
 [0],
 [7.4],
 [0.55],
 [-0.98],
 [0],
 [0],
 [0],
 [7.4],
 [0],
 [-0.98],
 [9.99],
 [0],
 [3.874],
 [7.4],
 [-0.35],
 [-0.98]]

P.S.: This could be done in many ways, but I find this one pretty good to understand.

CodePudding user response：

The Pythonic way would be to directly use a comprehension:

[lst if lst[0] == 0
     else displacement_gsj_values[displacement_gsj_match.index(lst)]
     for lst in displacement_all]

which gives as expected:

[[0], [0], [0], [-3.4], [0], [3.874], [0], [0], [0], [7.4], [0.55], [-0.98], [0],
 [0], [0], [7.4], [0], [-0.98], [9.99], [0], [3.874], [7.4], [-0.35], [-0.98]]