netCDF 为条件转换为 NaN答案

【问题标题】：netCDF convert to NaN for conditionalnetCDF 为条件转换为 NaN
【发布时间】：2016-08-31 19:19:03
【问题描述】：

当值大于零时，我想将 netCDF 文件中的值转换为名为 LandMask_NaN 的 NaN。但是，LandMask 与 numpy 将转换为 NaN 的类型之间似乎存在类型不匹配。非常感谢任何帮助，代码和信息如下：

 import netCDF4 as nc
 import numpy as np
 import matplotlib.pyplot as plt
 import csv as cs
 import pandas as pd

ncfile = nc.Dataset('C:\Users\mmso2\Google Drive\ENVI_I-PAC_2007_10_21_21_22_47.nc')#office machine

SARwind = ncfile.variables['sar_wind']
ModelWind = ncfile.variables['model_speed']
LON = ncfile.variables['longitude']
LAT = ncfile.variables['latitude']
LandMask = ncfile.variables['mask']

#clean the data of values = 70

SARwind_nan = SARwind[:].copy()
SARwind_nan[SARwind_nan == 0.0] = np.nan
SARwind_nan[SARwind_nan == 70.0] = np.nan

#clear the data of values where there is land
# % pos = land; neg = water

LandMask_NaN = LandMask[:].copy()
#LandMask_NaN[int(float(LandMask_NaN))]### will not convert
LandMask_NaN[LandMask_NaN >0.0] = np.nan #error here

我得到的错误是

#error
line 37, in <module>
LandMask_NaN[LandMask_NaN >= 0.0] = np.nan
ValueError: cannot convert float NaN to integer

尝试时

LandMask_NaN[int(float(LandMask_NaN))]

或

LandMask_NaN[float(int(LandMask_NaN))]

在尝试转换为 NaN 之前，我得到了

TypeError: only length-1 arrays can be converted to Python scalars

在检查我得到的 LandMask 类型时

<type 'netCDF4._netCDF4.Variable'>

我不知道如何找出变量类型？

更新：nc 变量的详细信息

NetCDF dimension information:
    Name: x
        size: 848
        type:       WARNING: x does not contain variable attributes
    Name: y
        size: 972
        type:       WARNING: y does not contain variable attributes
    Name: xfit
        size: 6
        type:       WARNING: xfit does not contain variable attributes
NetCDF variable information:
    Name: acquisition_time
        dimensions: ()
        size: 1.0
        type: dtype('float64')
        units: u'seconds since 2000-01-01 00:00:00'
        long_name: u'Acqusition time in Julian seconds since 2000-01-01T00:00:00Z'
        standard_name: u'time'
        calendar: u'gregorian'
    Name: nx
        dimensions: ()
        size: 1.0
        type: dtype('int32')
        units: u'1'
        long_name: u'Number of elements in this file'
    Name: ny
        dimensions: ()
        size: 1.0
        type: dtype('int32')
        units: u'1'
        long_name: u'Number of lines in this file'
    Name: nx0
        dimensions: ()
        size: 1.0
        type: dtype('int32')
        units: u'1'
        long_name: u'Number of elements in SIO file'
    Name: ny0
        dimensions: ()
        size: 1.0
        type: dtype('int32')
        units: u'1'
        long_name: u'Number of lines in SIO file'
    Name: nx00
        dimensions: ()
        size: 1.0
        type: dtype('int32')
        units: u'1'
        long_name: u'Number of elements in original SAR file'
    Name: ny00
        dimensions: ()
        size: 1.0
        type: dtype('int32')
        units: u'1'
        long_name: u'Number of lines in original SAR file'
    Name: xn
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'1'
        long_name: u'1'
    Name: yn
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'1'
        long_name: u'1'
    Name: line_size
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'm'
        long_name: u'Line size'
    Name: pixel_size
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'm'
        long_name: u'Pixel size'
    Name: model_time_js
        dimensions: ()
        size: 1.0
        type: dtype('float64')
        units: u'seconds since 2000-01-01 00:00:00'
        long_name: u'Model time julian seconds since 2000-01-01T00:00:00Z'
    Name: model_time_js_tau
        dimensions: ()
        size: 1.0
        type: dtype('float64')
        units: u'seconds since 2000-01-01 00:00:00'
        long_name: u'Model time plus tau julian seconds since 2000-01-01T00:00:00Z'
    Name: upper_left_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: upper_right_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: upper_left_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: upper_right_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: start_center_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: start_center_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: scene_center_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: scene_center_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: lower_left_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: lower_right_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: lower_left_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: lower_right_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: end_center_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: end_center_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: northernmost_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: southernmost_latitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'degrees'
    Name: easternmost_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: westernmost_longitude
        dimensions: ()
        size: 1.0
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'degrees'
    Name: nrcs_slope
        dimensions: ()
        size: 1.0
        type: dtype('float32')
    Name: nrcs_bias
        dimensions: ()
        size: 1.0
        type: dtype('float32')
    Name: sigma
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'1'
        long_name: u'Normalized Radar Cross Section.'
        coordinates: u'longitude latitude'
    Name: sar_wind
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'm s-1'
        long_name: u'SAR-derived wind speed at 10-m height neutral stability'
        standard_name: u'wind_speed'
        coordinates: u'longitude latitude'
    Name: input_dir
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'degrees'
        long_name: u'Interpolated directions used for wind inversion'
        coordinates: u'longitude latitude'
    Name: model_speed
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'm s-1'
        long_name: u'Interpolated model wind speed (=1 for non model directions)'
        standard_name: u'wind_speed'
        coordinates: u'longitude latitude'
    Name: mask
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('int16')
        units: u'1'
        long_name: u'Interpolated land mask distance from shore line. Positive values land / Negative value water'
        flag_values: array([-1,  0,  1], dtype=int16)
        flag_meanings: u'water shore land'
        coordinates: u'longitude latitude'
    Name: longitude
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'degrees_east'
        long_name: u'Longitude array in decimal degrees'
        standard_name: u'longitude'
    Name: latitude
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'degrees_north'
        long_name: u'Latitude array in decimal degrees'
        standard_name: u'latitude'
    Name: rlook
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'degrees'
        long_name: u'Radar look direction array in decimal degrees from North'
        coordinates: u'longitude latitude'
    Name: incid
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('float32')
        units: u'degrees'
        long_name: u'Incident angle array in degrees from nadir'
        coordinates: u'longitude latitude'
    Name: icemask
        dimensions: (u'y', u'x')
        size: 824256
        type: dtype('int16')
        units: u'1'
        long_name: u'Ice mask 0=no_data 1=water 2=land 3=sea_ice 4=snow'
        flag_values: array([0, 1, 2, 3, 4], dtype=int16)
        flag_meanings: u'no_data water land sea_ice snow'
        coordinates: u'longitude latitude'
    Name: lon_coef
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float64')
        units: u'1'
        long_name: u'Coefficients to compute longitude in degs from pixel/lines'
    Name: lon_xexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Longitude pixel exponents'
    Name: lon_yexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Longitude line exponents'
    Name: lat_coef
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float64')
        units: u'1'
        long_name: u'Coefficients to compute latitude in degs from pixel/lines'
    Name: lat_xexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Latitude pixel exponents'
    Name: lat_yexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Latitude line exponents'
    Name: i_coef
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float64')
        units: u'1'
        long_name: u'Coefficients to compute pixel from longitue/latitude'
    Name: i_xexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Pixel longitude exponents'
    Name: i_yexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Pixel latitude exponents'
    Name: j_coef
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float64')
        units: u'1'
        long_name: u'Coefficients to compute line from longitue/latitude'
    Name: j_xexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Line longitude exponents'
    Name: j_yexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Line latitude exponents'
    Name: incid_coef
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float64')
        units: u'1'
        long_name: u'Coefficients to compute incid in degs from pixel/lines'
    Name: incid_xexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Incid pixel exponents'
    Name: incid_yexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Incid line exponents'
    Name: rlook_coef
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float64')
        units: u'1'
        long_name: u'Coefficients to compute radar look direction in degs from pixel/lines'
    Name: rlook_xexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Radar look direction pixel exponents'
    Name: rlook_yexp
        dimensions: (u'xfit',)
        size: 6
        type: dtype('float32')
        units: u'1'
        long_name: u'Radar look direction line exponents'

【问题讨论】：

标签： python numpy nan netcdf4

【解决方案1】：

如果您共享 netcdf 文件会很有帮助，但这里有一些关于正在发生的事情的想法：

变量当前未作为 numpy 数组读入。您需要添加索引参数以将它们转换为数组。没有文件，我不确定它们是什么，但肯定有些是多维的。例如：

SARwind = ncfile.variables['sar_wind'][:,:]
ModelWind = ncfile.variables['model_speed'][:,:]
LON = ncfile.variables['longitude'][:]
LAT = ncfile.variables['latitude'][:]
LandMask = ncfile.variables['mask'][:,:]

然后您可以简单地将SARwind 分配给一个新变量SARWind_nan 并输入nan 值，就像您一直在做的那样。

SARWind_nan = SARwind
SARwind_nan[SARwind_nan == 0.0] = np.nan
SARwind_nan[SARwind_nan == 70.0] = np.nan

正确读入LandMask（我认为这很可能是2D，而不是您所拥有的1D），您可以类似地分配给新变量LandMask_nan 并输入nan 值。仔细检查LandMask 的类型，它可能是一个整数。 ncdump 或 ncks 是检查 netcdf 内容的好工具。

LandMask_NaN = LandMask
LandMask_NaN[LandMask_NaN > 0.0] = np.nan

【讨论】：

谢谢@N1B4。我会尝试一下。如何将我的 netCDF 文件附加到问题中？
你的建议很有道理，但我仍然有ValueError: cannot convert float NaN to integer的问题。我很高兴分享 netCDF 文件，但我不知道如何在这里分享？
如果可能，请将文件放在公共存储站点（例如 Dropbox）上，然后将链接粘贴到此处供我们访问。此外，提供文件的 ncdump 将有助于向我们展示变量和维度的详细信息。
很遗憾，我没有权限共享文件，但是我在上面的 nc 文件变量中添加了一些详细信息。
您可以只发布文件的 sn-p 吗？不需要全部，只需要几个网格单元即可。否则，向我们展示其内容的 ncdump 也会有所帮助。