FLAV10 - 1 year ago 63

Python Question

I have a csv file of data from a LiDAR sensor that looks like this, but with a bagillion more lines:

`scan_0,scan_1,scan_2`

timestamp_0,timestamp_1,timestamp_2

7900200,7900225,7900250

logTime_0,logTime_1,logTime_2

27:46.8,27:46.8,27:46.8

distance_0,distance_0,distance_0

132,141,139

136,141,155

139,141,155

138,143,155

138,143,142

139,143,136

138,143,136

This is data from a planar sensor. So Scan_0 is a list or "radial" coordinates for the specific scan at a time stamp.

My plan is to:

- Read the CSV file into a list
- Transpose the list
- Turn each element of row into a xyz format like the example below.

`scan_0 -----> scan_0`

timestamp_0-> timestamp_0

7900200-----> 7900200

logTime_0---> logTime_0

27:46.8-----> 27:46.8

distance_0--> distance_0

132---------> [132*cos(1),132*sin(1),7900200]

136---------> [136*cos(2),136*sin(2),7900200]

139---------> [139*cos(3),139*sin(3),7900200]

138---------> . .

138---------> . .

139---------> . .

138---------> [138*cos(7),139*sin(7),7900200]

- Write the array of xyz coordinates to a new csv file with one coordinate per line'
- eventually use a trajectory instead of timestamp for the z coordinate from another csv file.

I tell you all of this, so you have some context for my motivation.

here is what I have so far:

`import csv`

import numpy

from numpy import genfromtxt

from numpy import vsplit

import math

with open('2016_09_16_14_29_09_953.csv',"r") as f:

reader = csv.reader(f,delimiter = ",")

data = list(reader)

row_count = len(data)

print row_count

with open("out.csv", "a") as f1:

my_r = genfromtxt('2016_09_16_14_29_09_953.csv', delimiter=',', skip_header=6, autostrip=True) #import data

my_r = my_r.T #transpose

for x in my_r:

i=0

while i < row_count/360:

x = [x*math.cos(i), x*math.sin(i), i]

i = i + row_count/360

thedatawriter = csv.writer(f1) #setup writer

for row in my_r: #write the data

thedatawriter.writerow(row)

All this really does it ouput the transpose of the source file. It appears that I am having trouble turning the single entry in the list into a list itself. What am I doing wrong here? Any help, advice, and guidance is greatly appreciated.

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Answer Source

The problem that you have is that you are trying to assign new value to variable that does not reference to array.

So you have

```
for x in my_r:
i=0
while i < row_count/360:
x = [x*math.cos(i), x*math.sin(i), i]
i = i + row_count/360
```

You cannot do that, because x is not actual element of `my_r`

list(changing `x`

would not lead to changing element on `my_r`

).

The simplest way is to create new array to store desired values.

```
my_r = genfromtxt('2016_09_16_14_29_09_953.csv', delimiter=',', skip_header=6, autostrip=True) #import data
my_r = my_r.T #transpose
new_r = []
for x in my_r:
i=0
while i < row_count/360:
new_r.append([x*math.cos(i), x*math.sin(i), i])
i = i + row_count/360
thedatawriter = csv.writer(f1) #setup writer
for row in new_r: #write the data
thedatawriter.writerow(row)
```

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