Python: Replacing every number in an array with a different number

Question

I have data that is in the below format (in an ASCII file):

363 28 24 94

536 28 24 95

where we have speed, time, lat, long. Time, lat and long values are all codes for the true values. For example a time of 28 corresponds to 2015-02-01, lat of 24 corresponds to a true latitude of -67 etc.

There are many different coded values. Time ranges from 0-28, lat from 0-24 and long from 0-108.

I would like the replace every single one of the 'code' values with their true counterpart and output into a text file. The format of the text file would be speed, true time, true lat, true long.

I have tried doing this by using a dictionary and replace, however replace does not seem to like the fact that I am reading in an array.

I should also mention that the input file with the original format shown above is 79025 lines long and for each line I have to replace 3 values.

This is my current attempt which is not working with error message: AttributeError: 'numpy.ndarray' object has no attribute 'replace'

data=np.genfromtxt('./data/u_edit_2.coords')
time=data[:,[1]]
lat=data[:,[2]]
lon=data[:,[3]]
def replace_all(text, dic):
     for i, j in dic.iteritems():
         text = text.replace(i, j)
     return text
reps = {'0':'2015-01-02', '1':'23773', '2':'23774'}
time_new = replace_all(time, reps)
print time_new

Any suggestions would be appreciated, cheers.

If the codes translate to actual values through simple functions, that would be a more effective way to do the translation. How are the codes related to the values? — Frank M
– Frank M, Commented Dec 4, 2015 at 16:10

perimosocordiae · Accepted Answer · 2015-12-04 16:44:56Z

3

Your codes look like indices, so you could use some numpy index tricks to get your result:

# your values go here, where lat_values[24] = -67, etc.
time_values = np.array(['2015-01-01', '2015-01-02', ...])
lat_values = np.array([...])
lon_values = np.array([...])

# read the coded coords
_, time, lat, lon = np.loadtxt('coords', dtype=int).T

# decode
time = time_values[time]
lat = lat_values[lat]
lon = lon_values[lon]

answered Dec 4, 2015 at 16:44

perimosocordiae

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Comments

Alan · Accepted Answer · 2015-12-04 16:44:58Z

This looks to be better handled as a file processing issue. You can then process the file once and read in the processed data whenever needed, without additional processing.

fmt = "{},{},{},{}\n"  #or whatever format you want
def transform(line):
  speed, time, lat, lon = line.strip().split()
  return fmt.format(
    speed,
    true_time(time),
    true_lat(lat),
    true_lon(lon)
  )

#change the next three functions to fit your needs
def true_time(time):
  return time
def true_lat(lat):
  return lat
def true_lon(lon):
  return lon

fin = open("c:/temp/temp.txt","r")
fout = open("c:/temp/temp2.txt","w")
for line in fin:
  if line.strip(): #ignore empty lines
    fout.write(transform(line))

fin.close()
fout.close()

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