ValueError setting an array element with a sequence

Question

I am getting this error:

File "mypath\mypythonscript.py", line 3484, in secondfunction
RRDuringArray = p.array(UnFilteredDuringExSummaryOfMeansArray,dtype=p.float64)[1:,3]
ValueError: setting an array element with a sequence.

When I run this python code:

import numpy as p

def firstfunction():
    UnFilteredDuringExSummaryOfMeansArray = []
    MeanOutputHeader=['TestID','ConditionName','FilterType','RRMean','HRMean',
                      'dZdtMaxVoltageMean','BZMean','ZXMean','LVETMean','Z0Mean',
                      'StrokeVolumeMean','CardiacOutputMean','VelocityIndexMean']
    dataMatrix = BeatByBeatMatrixOfMatrices[column]
    roughTrimmedMatrix = p.array(dataMatrix[1:,1:17])

    trimmedMatrix = p.array(roughTrimmedMatrix,dtype=p.float64)  #ERROR THROWN HERE

    myMeans = p.mean(trimmedMatrix,axis=0,dtype=p.float64)
    conditionMeansArray = [TestID,testCondition,'UnfilteredBefore',myMeans[3], myMeans[4], 
                           myMeans[6], myMeans[9], myMeans[10], myMeans[11], myMeans[12],
                           myMeans[13], myMeans[14], myMeans[15]]
    UnFilteredDuringExSummaryOfMeansArray.append(conditionMeansArray)
    secondfunction(UnFilteredDuringExSummaryOfMeansArray)
    return

def secondfunction(UnFilteredDuringExSummaryOfMeansArray):
    RRDuringArray = p.array(UnFilteredDuringExSummaryOfMeansArray,dtype=p.float64)[1:,3]
    return

firstfunction()

Can someone explain to me how to fix this problem? 

Answer 1

The problem is the shape of the input list isn't a (generalized) "box" that can be turned into a multidimensional array. This error can also happen when you are trying to use a string as an element in an array of type float:

numpy.array([1.2, "abc"], dtype=float)   # wrong!

To solve this,  you could use the dtype object, which enables the array to hold arbitrary Python objects:

numpy.array([1.2, "abc"], dtype=object)

I hope this helps you.